C&S MRN3 Manuale utente

High-Tech Range

MRN3- Mains decoupling Relay

C&S Protection & Control Ltd.

TRIP

ENTER

SELECT/RESET

U<<

1/3

U>>

MRN3-1

D/Y

max

min

U>>

U<<

Contents

1. Introduction and application

2. Features and characteristics

3. Design

3.1 Connections

3.1.1 Analog input circuits

3.1.2 Blocking input

3.1.3 Reset input

3.1.4 Output relays

3.1.5 Fault recorder

3.2 Parameter settings

3.3 LEDs

3.4 Front plate

4. Working principle

4.1 Analog circuits

4.2 Digital circuits

4.3 Voltage supervision

4.3.1 Selection of star or delta connection

4.4 Principle of frequency supervision

4.5 Measuring of frequency gradient (MRN3-2)(MRN3-2)

(MRN3-2)(MRN3-2)

(MRN3-2)

4.6 Vector surge supervision (MRN3-1)(MRN3-1)

(MRN3-1)(MRN3-1)

(MRN3-1)

4.6.1 Measuring principle of vector surge

supervision

4.7 Voltage threshold value for frequency

measuring

4.8 Blocking function

5. Operation and settings

5.1 Display

5.2 Setting procedure

5.3 Systemparameter

5.3.1 Display of residual voltage UEas primary

quantity (Uprim/Usec)

5.3.2 Δ/Y - Switch over

5.3.3 Setting of nominal frequency

5.3.4 Display of the activation storage (FLSH/

NOFL)

5.3.5 Parameterswitch / external trigger for the

fault recorder

5.4 Protection parameters

5.4.1 Parameter setting of over and under-

voltage supervision

5.4.2 Number of measuring repetitions (T) for

frequency functions

5.4.3 Threshold of frequency supervision

5.4.4 Tripping delays for the frequency elements

5.4.5 Parameter setting of vector surge

supervision (MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1)

5.4.6 Parameter setting of frequency gradient

(MRN3-3MRN3-3

MRN3-3MRN3-3

MRN3-3)

5.4.7 Voltage threshold value for frequency and

vector surge measuring (df/dt at MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2)

5.4.8 Adjustment of the slave address

5.4.9 Setting of Baud-rate (applies for Modbus

Protocol only)

5.4.10 Setting of parity (applies for Modbus

Protocol only)

5.5 Adjustment of the fault recorder

5.5.1 Number of the fault recordings

5.5.2 Adjustment of trigger occurences

5.5.3 Pre-trigger time (Tpre)

5.6 Adjustment of the clock

5.7 Additional functions

5.7.1 Setting procedure for blocking the

protection functions

5.8 Indication of measuring values

5.8.1 Measuring indication

5.8.2 Min./Max. values

5.8.3 Unit of the measuring values displayed

5.8.4 Indication of fault data

5.9 Fault memory

5.9.1 Reset

5.9.2 Erasure of fault storage

6. Relay testing and commissioning

6.1 Power-On

6.2 Testing the output relays

6.3 Checking the set values

6.4 Secondary injection test

6.4.1 Test equipment

6.5 Example of test circuit

6.5.1 Checking the input circuits and measuring

functions

6.5.2 Checking the operating and resetting values

of the over/undervoltage functions

6.5.3 Checking the relay operating time of the

over/undervoltage functions

6.5.4 Checking the operating and resetting values

of the over/underfrequency functions

6.5.5 Checking the relay operating time of the

over/underfrequency functions

6.5.6 Checking the vector surge function

6.5.7 Checking the external blocking and reset

functions

6.6 Primary injection test

6.7 Maintenance

7. Technical data

7.1 Measuring input circuits

7.2 Common data

7.3 Setting ranges and steps

7.3.1 Interface parameter

7.3.2 Parameters for the fault recorder

7.4 Output relays

8 Order form

1. Introduction and application

The MRN3MRN3

MRN3MRN3

MRN3 is a universal mains decoupling device and

covers the protection requirements from VDEW and most

other utilities for the mains parallel operation of power

stations.

zOver/ and undervoltage protection

zOver/ and underfrequency protection

zExtremely fast decoupling of generator in case of

mains failure ((

((

(MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1))

))

) or

zRate of change of frequency df/dt ((

((

(MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2))

))

)

Because of combination of three protectional functions in

one device the MRN3MRN3

MRN3MRN3

MRN3 is a very compact mains de-

coupling device. Compared to the standardly used single

devices it has a very good price/performance ratio.

For applications where the single protection functions are

required CSPCCSPC

CSPCCSPC

CSPC can offer the single MRMR

MRMR

MR-relays as follows:

zMRU3-1MRU3-1

MRU3-1MRU3-1

MRU3-1 four step independent over-/ and

undervoltage protection (also used for

generator earth fault protection)

zMRU3-2MRU3-2

MRU3-2MRU3-2

MRU3-2 two step independent over-/ and

undervoltage protection with

evaluation of the symmetrical voltage

components

zMRF3MRF3

MRF3MRF3

MRF3 four step independent over/ and

underfrequency protection and two

step frequency gradient supervision

df/dt

zMRG2MRG2

MRG2MRG2

MRG2 generator mains monitor / vector

surge detection

2. Features and characteristics

zMicroprocessor technology with watchdog,

zeffective analog low pass filter for suppressing

harmonics when measuring frequency and vector

surge,

zdigital filtering of the measured values by using

discrete Fourier analysis to suppress higher

harmonics and d.c. components induced by faults or

system operations

zintegrated functions for voltage, frequency and vector

surge in one device as well as single voltage,

frequency and vector surge devices,

ztwo parameter sets,

zvoltage supervision each with two step under-/ and

overvoltage detection

zFrequency supervision with three step under-/ or

overfrequency (user setting)

zCompletely independent time settings for voltage and

frequency supervision

zadjustable voltage threshold value for blocking

frequency and vector surge measuring.

zdisplay of all measuring values and setting

parameters for normal operation as well as tripping

via a alphanumerical display and LEDs

zdisplay of measuring values as primary quantities

zStorage of trip values and switching-off time (tCBFP) of

5 fault occurences (fail-safe of voltage),

zrecording of up to eight fault occurences with time

stamp

zfor blocking the individual functions by the external

blocking input, parameters can be set according to

requirement,

zuser configurable vector surge measurement 1-of-3

or 3-of-3,

zreliable vector surge measuring by exact calculation

algorithm

zsuppression of indication after an activation (LED

flash),

zfree assignment for output relays,

zdisplay of date and time,

zin complience with VDE 0435, part 303 and IEC

255,

zserial data exchange via RS485 interface possible;

alternatively with CSPC RS485 Pro-Open Protocol or

Modbus Protocol.

3.1.1 Analog input circuits

The analog input voltages are galvanically decoupled by

the input transformers of the device, then filtered and

finally fed to the analog digital converter. The measuring

circuits can be applied in star or delta connection (refer

to chapter 4.3.1).

3.1.2 Blocking input

The blocking function can be set according to

requirement. By applying the auxiliary voltage to D8/E8,

the previously set relay functions are blocked (refer to

4.8 and 5.7.1).

3.1.3 Reset input

Please refer to chapter 5.9.1

3.1.4 Output relays

The MRN3MRN3

MRN3MRN3

MRN3 is equipped with 5 output relays. Apart from

the relay for self-supervision, all protective functions can

be optionally assigned :

zRelay 1 : C1, D1, E1 and C2, D2, E2

zRelay 2 : C3, D3, E3 and C4, D4, E4

zRelay 3 : C5, D5, E5

zRelay 4 : C6, D6, E6

zRelay 5 : Signal self supervision (internal fault of the

unit) C7, D7, E7

All trip and alarm relays are working current relays, the

relay for self supervision is an idle current relay.

3.1.4 Output relays

The MRN3MRN3

MRN3MRN3

MRN3 has a fault value recorder which records the

measured analog values as instantaneous values.

The instantaneous values

UL1; UL2; UL3; for star connection

or U12; U23; U21 for delta connection

are scanned at a raster of 1.25 ms (at 50 Hz) and

possible to store 1-8 fault occurences with a total

recording time of 16 s (with 50 Hz) and 13.33 s (with 60

Hz) per channel.

Fig. 3.1 : Connection diagram MRN3-1 and MRN3-2Fig. 3.1 : Connection diagram MRN3-1 and MRN3-2

Fig. 3.1 : Connection diagram MRN3-1 and MRN3-2

Storage division

Independent of the recording time, the entire storage

capacity can be divided int0 several cases of disturbance

with a shorter recording time each. In addition, the

deletion behaviour of the fault recorder can be

influenced.

No writing over

If 2, 4 or 8 recordings are chosen, the complete memory

is divided into the relevant number of partial segments. If

this max. number of fault event has been exceeded, the

fault recorder block any further recordings in order to

prevent that the stored data are written over. After the

data have been read and deleted, the recorder to ready

again for further action.

Writing over

If 1, 3, or 7 recordings are chosen, the relevant number

of partial segments is reserved in the complete memory.

If the memory is full, a new recording will always write

over the oldest one.

The memory part of the fault recorder is designed as

circulating storage. In this example 7 fault records can be

stored (written over).

Fig. 3.2 : Division of the memory into 8 segments,Fig. 3.2 : Division of the memory into 8 segments,

Fig. 3.2 : Division of the memory into 8 segments,

for examplefor example

for example

Memory space 6 to 4 is occupied.

Memory space 5 is currently being written in

tdt

tf</tf>

f<</f>>

f</f>

tf<</tf>>

tu<</tu>>

E8D8CB

Blocking

input

External

Reset

L3L2L1

Serial Interface

selfsupervision

Alarm

Relay 1

L-/N

L+/L

U</U>

U<</U>>

TRIP

ENTER

SLECT/

REST

tu</tu>

Power

supply

Relay 2

Relay 3

Relay 4

3. Design

3.1 Connections

Blocking function

Parameter Settingarameter Setting

arameter Settingarameter Setting

arameter Setting MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2

U< X X

U<< X X

U> X X

U>> X X

f1 X X

f2 X X

f3 X X

ΔΘ X

df/dt X

Table 3.3 : Blocking functionable 3.3 : Blocking function

able 3.3 : Blocking functionable 3.3 : Blocking function

able 3.3 : Blocking function

Parameters for the fault recorder

Parameter Settingarameter Setting

arameter Settingarameter Setting

arameter Setting MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2

Number of fault X X

events

Trigger events X X

Pre-Triggerzeit Tpre XX

Table 3.4 : Parameters for the fault recorderable 3.4 : Parameters for the fault recorder

able 3.4 : Parameters for the fault recorderable 3.4 : Parameters for the fault recorder

able 3.4 : Parameters for the fault recorder

Additional functions

Parameter Settingarameter Setting

arameter Settingarameter Setting

arameter Setting MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2

Relay assignment X X

Fault recorder X X

Table 3.5 : Additional functionsable 3.5 : Additional functions

able 3.5 : Additional functionsable 3.5 : Additional functions

able 3.5 : Additional functions

Date and time

Parameter Settingarameter Setting

arameter Settingarameter Setting

arameter Setting MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2

Year Y = 99 X X

Month M = 03 X X

Day D = 16 X X

hour h = 07 X X

minute m = 29 X X

second s = 56 X X

Table 3.6 : Date and timeable 3.6 : Date and time

able 3.6 : Date and timeable 3.6 : Date and time

able 3.6 : Date and time

The window for parameter setting is located behind the

measured value display. The parameter window can be

accessed via the <SELECT/RESET> key.

3.2 Parameter settings

System parameter

Parameter Settingarameter Setting

arameter Settingarameter Setting

arameter Setting MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2

Uprim/Usek XX

Δ/Y X X

fN X X

P2/FR X X

LED-Flash X X

Table 3.1 : System parametersable 3.1 : System parameters

able 3.1 : System parametersable 3.1 : System parameters

able 3.1 : System parameters

Protection parameters

Setting parameterSetting parameter

Setting parameter MRMR

MRMR

MRN3-1N3-1

N3-1N3-1

N3-1 MRN3-2MRN3-2

MRN3-2MRN3-2

MRN3-2

U< X X

tU< XX

U<< X X

tU<< XX

U> X X

tU> XX

U>> X X

tU>> XX

TXX

f1XX

tf1 XX

f2XX

tf2 XX

f3XX

tf3 XX

df X

dt X

1/3 X

ΔΘ X

UB<XX

RS485/Slave X X

Baud-Rate* X X

Parity-Check* X X

Table 3.2: Protection parametersable 3.2: Protection parameters

able 3.2: Protection parametersable 3.2: Protection parameters

able 3.2: Protection parameters

* only Modbus

Since memory spaces 6, 7 and 8 are occupied, this

example shows that the memory has been assigned more

than eight recordings. This means that No. 6 is the oldest

fault recording and No. 4 the most recent one.

trigger occurrence

recording duration

pre

[s]

Fig. 3.3 : Basic set-up of the fault recorderFig. 3.3 : Basic set-up of the fault recorder

Fig. 3.3 : Basic set-up of the fault recorder

Each memory segment has a specified storage time which

permits setting of a time prior to the trigger event.

Via the interface RS485 the data can be read and

processed by means of a PC (HTL/PL-Soft4). The data is

graphically edited and displayed. Binary tracks are

recorded as well, e.g. activation and trip.

4. Working principle

4.1 Analog circuits

The input voltages are galvanically insulated by the input

transformers. The noise signals caused by inductive and

capacitive coupling are supressed by an analog R-C filter

circuit.

The analog voltage signals are fed to the A/D-converter

of the microprocessor and transformed to digital signals

through Sample- and Hold- circuits. The analog signals

are sampled with a sampling frequency of 16 x fN,

namely, a sampling rate of 1.25 ms for every measuring

quantity, at 50 Hz.

4.2 Digital circuits

The essential part of the MRN3MRN3

MRN3MRN3

MRN3 relay is a powerful

microcontroller. All of the operations, from the analog

digital conversion to the relay trip decision, are carried

out by the microcontroller digitally. The relay program is

located in an EPROM (Electrically-Programmable-Read-

Only-Memory). With this program the CPU of the

microcontroller calculates the three phase voltage in

order to detect a possible fault situation in the protected

object.

For the calculation of the voltage value an efficient digital

filter based on the Fourier Transformation (DFFT-Discrete

Fast Fourier Transformation) is applied to suppress high

frequency harmonics and d.c. components caused by

fault-induced transients or other system disturbances. The

microprocessor continuously compares the measured

values with the preset thresholds stored in the parameter

memory (EEPROM). If a fault occures an alarm is given

and after the set tripping delay has elapsed, the

corresponding trip relay is activated.

The relay setting values for all parameters are stored in

a parameter memory (EEPROM - Electrically Erasable

Programmable Read Only Memory), so that the actual

relay settings cannot be lost, even if the power supply is

interrupted.

The microprocessor is supervised by a built-in “watchdog”

timer. In case of a failure the watchdog timer resets the

microprocessor and gives an alarm signal via the output

relay “self supervision”.

4.3 Voltage supervision

The voltage element of MRN3MRN3

MRN3MRN3

MRN3 has the application in

protection of generators, consumers and other electrical

equipment against over/and undervoltage. The relay is

equipped with a two step independent three-phase

overvoltage (U>, U>>) and undervoltage (U<, U<<)

function with completely separate time and voltage

settings.

In delta connection the phase-to-phase voltages and in

star connection the phase-to-neutral voltages are

continuously compared with the preset thresholds.

For the overvoltage supervision the highest, for the

undervoltage supervision the lowest voltage of the three

phases are decisive for energizing.

3.3 LEDs

All LEDs (except LED RS, min. and max.) are two-

coloured. The LEDs on the left side, next to the alpha-

numerical display light up green during measuring and

red after tripping.

The LEDs below the push button <SELECT/RESET> are lit

green during setting and inquiry procedure of the setting

values which are printed on the left side next to the LEDs.

The LEDs will light up red after parametrizing of the

setting values next to their right side.

The LED marked with letters RS lights up during setting of

the slave address of the device for serial data

communication.

The LED marked with the letters FR is alight while the fault

recorder is being adjusted.

3.4 Front plate

TRIP

ENTER

SELECT/RESET

U<<

1/3

U>>

MRN3-1

D/Y

max

min

f1tf1

tf2

tf3

tU>>

tU<<

tU<

tU>

TRIP

ENTER

SELECT/RESET

U<<

U>>

MRN3-2

D/Y

max

min

U>>

U<<

Fig. 3.5 : Front plate MRN3-2Fig. 3.5 : Front plate MRN3-2

Fig. 3.5 : Front plate MRN3-2

Fig. 3.4 : Front plate MRN3-1Fig. 3.4 : Front plate MRN3-1

Fig. 3.4 : Front plate MRN3-1

4.3.1 Selection of star or delta connection

All connections of the input voltage transformers are led

to screw terminals. The nominal voltage of the device is

equal to the nominal voltage of the input transformers.

Dependent on the application the input transformers can

be connected in either delta or star. The connection for

the phase-to-phase voltage is the delta connection. In star

connection the measuring voltage is reduced by 1/√3.

During parameter setting the connection configuration

either Y or Δhas to be adjusted.

Fig. 4.1: Input v.t.s in delta connectionFig. 4.1: Input v.t.s in delta connection

Fig. 4.1: Input v.t.s in delta connection ((

((

(ΔΔ

ΔΔ

Δ))

))

)

Fig. 4.2: Input v.t.s in star connection (Y)Fig. 4.2: Input v.t.s in star connection (Y)

Fig. 4.2: Input v.t.s in star connection (Y)

4.4 Principle of frequency supervision

The frequency element of MRN3 protects electrical

generators, consumers or electrical operating equipment

in general against over- or underfrequency. The relay

has independent three frequency elements f1- f3with a

free choice of parameters, with separate adjustable

pickup values and delay times.

The measuring principle of the frequency supervision is

based on the time measurement of complete cycles,

whereby a new measurement is started at each voltage

zero passage. The influence of harmonics on the

measuring result is thus minimized.

Fig. 4.3: Determination of cycle duration byFig. 4.3: Determination of cycle duration by

Fig. 4.3: Determination of cycle duration by

means of zero passagesmeans of zero passages

means of zero passages.

In order to avoid false tripping during occurence of

interference voltages and phase shifts the relay works with

an adjustable measuring repetition (see chapter 5.4.2)

Frequency tripping is sometimes not desired by low

measured voltages which for instance occur during

alternator acceleration. All frequency supervision

functions can be blocked with the aid of an adjustable

voltage threshold UBin case the measured voltage value

is below this value.

4.5 Measuring of frequency gradient

(MRN3-2)

Electrical generators running in parallel with the mains,

e.g. industrial internal power supply plants, should be

separated from the mains when failure in the intrasystem

occurs for the following reasons:

zIt must be prevented that the electrical generators are

damaged when mains voltage recovering

asynchrone, e.g. after a short interruption.

zThe industrial internal power supply must be

maintained.

A reliable criterion of detecting mains failure is the

measurement of the rate of change of frequency df/dt.

Precondition for this is a load flow via the mains coupling

point. At mains failure the load flow changing then

spontaneously leads to an increasing or decreasing

frequency. At active power deficit of the internal power

station a linear drop of the frequency occurs and a linear

increase occurs at power excess. Typical frequency

gradients during application of “mains decoupling” are in

the range of 0.5 Hz/s up to over 2 Hz/s. The MRN3

detects the instantaneous frequency gradient df/dt of each

mains voltage period in an interval of one half period

each. Through multiple evaluation of the frequency

gradient in sequence the continuity of the directional

change (sign of the frequency gradient) is determined.

Because of this special measuring procedure a high safety

in tripping and thus a high stabilty against transient

processes, e.g. switching procedure are reached. The

total switching off time at mains failure is between 60 ms

and 80 ms depending on the setting.

Sec. Winding of

mains V.T.

U31

U23

U12

CA7

Sec. Winding of

mains V.T.

u(t) T

The rotor displacement angle ϑbetween stator and rotor

is depending of the mechanical moving torque of the

generator shaft. The mechanical shaft power is balanced

with the electrical feeded mains power, and therefore the

synchronous speed keeps constant (Fig. 4.5).

Fig. 4.5: Voltage vectors at mains parallelFig. 4.5: Voltage vectors at mains parallel

Fig. 4.5: Voltage vectors at mains parallel

operationoperation

operation

4.6 Vector surge supervision (MRN3-1)

The vector surge supervision protects synchronous

generators in mains parallel operation due to very fast

decoupling in case of mains failure. Very dangerous are

mains auto reclosings for synchronous generators. The

mains voltage returning after 300 ms can hit the

generator in asynchronous position. A very fast

decoupling is also necessary in case of long time mains

failures. Generally there are two different applications:

a) Only mains parallel operation no singleOnly mains parallel operation no single

Only mains parallel operation no singleOnly mains parallel operation no single

Only mains parallel operation no single

operation:operation:

operation:

In this application the vector surge supervision

protects the generator by tripping the generator

circuit breaker in case of mains failure.

b) Mains parallel operation and singleMains parallel operation and single

Mains parallel operation and singleMains parallel operation and single

Mains parallel operation and single

operation:operation:

operation:

For this application the vector surge supervision trips

the mains circuit breaker. Here it is insured that the

gen.-set is not blocked when it is required as the

emergency set.

A very fast decoupling in case of mains failures for

synchronous generators is known as very difficult. Voltage

supervision units cannot be used because the synchronous

alternator as well as the consumer impedance support the

decreasing voltage.

For this the mains voltage drops only after some 100 ms

below the pickup threshold of voltage supervision relays

and therefore a safe detection of mains auto reclosings is

not possible with this kind of relay.

Frequency relays are partial unsuitable because only a

highly loaded generator decreases its speed within 100

ms. Current relays detect a fault only when shortcircuit

type currents exist, but cannot avoid their development.

Power relays are able to pickup within 200 ms, but they

cannot prevent power to rise to short-circuit values too.

Since power changes are also caused by sudden loaded

alternators, the use of power relays can be problematic.

Whereas the MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 detects mains failures within 60

ms without the restrictions described above because they

are specially designed for applications where very fast

decoupling from the mains is required.

Adding the operating time of a circuit breaker or contactor,

the total disconnection time remains below 150 ms. Basic

requirement for tripping of the generator/mains monitor

is a change in load of more than 15 - 20 % of the rated

load. Slow changes of the system frequency, for instance

at regulating processes (adjustment of speed regulator) do

not cause the relay to trip.

Trippings can also be caused by short-circuits within the

grid, because a voltage vector surge higher than the

preset value can occur. The magnitude of the voltage

vector surge depends on the distance between the short-

circuit and the generator. This function is also of

advantage to the Power Utility Company because the

mains short-circuit capacity and consequently the energy

feeding the short-circuit is limited.

To prevent a possible false tripping the vector surge

measuring can be blocked at a set low input voltage (refer

to 5.4.7). The undervoltage lockout acts faster then the

vector surge measurement.

Vector surge tripping is blocked by a phase loss so that a

VT fault (e.g. faulty VTs fuse) does not cause false tripping.

When switching on the aux. voltage or measuring voltage,

the vector surge supervision is blocked for 5 s (refer to

chapter 4.8).

Note:Note:

Note:

In order to avoid any adverse interference voltage effects,

for instance from contactors or relays, which may cause

overfunctions, MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 should be connected separately

to the busbar.

4.6.1 Measuring principle of vector surge

supervision

When a synchronous generator is loaded, a rotor

displacment angle is build between the terminal voltage

(mains voltage U1) and the synchronous internal voltage

(Up). Therefore a voltage difference ΔU is built between

Up and U1 (Fig. 4.4).

Fig. 4.4: Equivalent circuit at synchronousFig. 4.4: Equivalent circuit at synchronous

Fig. 4.4: Equivalent circuit at synchronous

generator in parallel with the mainsgenerator in parallel with the mains

generator in parallel with the mains

ΔU= .jX

U1Z

Mains

ΔU= l

.jX

Generator Mains / Load

Fig. 4.6: Equivalent circuit at mains failureFig. 4.6: Equivalent circuit at mains failure

Fig. 4.6: Equivalent circuit at mains failure

Fig. 4.7: Voltage vectors at mains failureFig. 4.7: Voltage vectors at mains failure

Fig. 4.7: Voltage vectors at mains failure

In case of mains failure or auto reclosing the generator

suddenly feeds a very high consumer load. The rotor

displacement angle is decreased repeatedly and the

voltage vector U1changes its direction (U1‘) (Fig. 4.6 and

4.7).

Fig. 4.8: Voltage vector surgeFig. 4.8: Voltage vector surge

Fig. 4.8: Voltage vector surge

As shown in the voltage/time diagram the instantaneous

value of the voltage jumps to another value and the phase

position changes. This is named phase or vector surge.

The MRN3-1MRN3-1

MRN3-1MRN3-1

MRN3-1 measures the cycle duration. A new

measuring is started at each voltage zero passage. The

measured cycle duration is internally compared with a

quartz stable reference time and from this the deviation

of the cycle duration of the voltage signal is ascertained.

In case of a vector surge as shown in fig. 4.8, the zero

Application hint

Although the vector surge relay guarantees very fast and

reliable detection of mains failures under nearly all

operational conditions of mains parallel running

alternators, the following borderline cases have to be

considered accordingly:

a) None or only insignificant change of power flow at the

utility connection point during mains failures.

This can occur during peak lopping operation or in CHP

stations (Combined Heat and Power) where the power

flow between power station and the public grid may be

very low. For detection of a vector surge at parallel

running alternators, the load change must be at least 15

- 20 % of the rated power. If the active load at the utility

connection point is regulated to a minimal value and a

high resistance mains failure occurs, then there are no

vector surge nor power and frequency changes and the

mains failure is not detected.

This can only happen if the public grid is disconnected

near the power station and so the alternators are not

additionally loaded by any consumers. At distant mains

failures the synchronous alternators are abruptly loaded

by remaining consumers which leads directly to a vector

surge and so mains failure detection is guaranteed.

If such a situation occurs the following has to be taken into

account:

In case of an undetected mains failure, i.e. with the mains

coupling C.B. closed, the vector surge relay reacts upon

the first load change causing a vector surge and trips the

mains C.B.

For detecting high resistance mains failures a minimum

current relay with an adjustable trip delay can be used. A

trip delay is needed to allow regulating actions where the

current may reach “zero” at the utility connection point.

At high resistance mains failures, the mains coupling C.B.

is tripped by the minimum current relay after the time

delay.

To prevent asynchronous switching on, an automatic

reclosing of the public grid should be not possible during

this time delay.

passage occurs either earlier or later. The established

deviation of the cycle duration is in compliance with the

vector surge angle.

If the vector surge angle exceeds the set value, the relay

trips immediately.

Tripping of the vector surge is blocked in case of loss of

one or more phases of the measuring voltage.

Tripping logic for vector surge measurement:ripping logic for vector surge measurement:

ripping logic for vector surge measurement:ripping logic for vector surge measurement:

ripping logic for vector surge measurement:

The vector surge function of the MRN3-1 supervises vector

surges in all three phases at the same time. Tripping of the

relay can be adjusted for one phase vector surge (more

sensitive measurement). For this the parameter 1/3 has

to be set to “1Ph”. When the parameter 1/3 is set to

“3Ph”, tripping of the vector surge element occurs only if

the vector surge angle exceeds the set value in all three

phases at the same time.

UP~

ΔU’= l’

1.jXdl’1

U’

Mains

Load

Generator

U’1

ΔU’= l’

.jXd

U(t)

Voltage vector surge

(t) u ’(t)

Trip

Dt~ DQ

4.7 Voltage threshold value for frequency

measuring

At low measuring voltages, e.g. during generator start-

up, frequency and vector surge or df/dt-measuring is

perhaps not desired.

By means of the adjustable voltage threshold value UB<,

functions f1- f3, df/dt or ΔΘ are blocked if the measured

voltage falls below the set value.

Blocking function set in compliance with require-

ments :

The MRN3MRN3

MRN3MRN3

MRN3 has an external blocking input. By applying

the auxiliary voltage to input D8/E8, the requested

protection functions of the relay are blocked (refer to

5.7.1).

A further measure could be, that the load regulation at

the utility connection point guarantees a minimum power

flow of 15 - 20 % of rated power.

b) Short circuit type loading of the alternators at distant

mains failures

At any distant mains failure, the remaining consumers

cause sudden short circuit type loading of the power

station generators. The vector surge relay detects the

mains failure in about 60 ms and switches off the mains

coupling C.B. The total switch off time is about 100 - 150

ms. If the generators are provided with an extremely fast

1010

4.8 Blocking function

No.No.

No. DynamicDynamic

DynamicDynamic

Dynamic BehaviourBehaviour

BehaviourBehaviour

Behaviour U</<<U</<<

U</<<U</<<

U</<< U>/>>U>/>>

U>/>>U>/>>

U>/>> ff

f11

1, f, f

, f, f

, f22

2, f, f

, f, f

, f33

3ΔΔ

ΔΔ

ΔΘΘ

ΘΘ

Θdf/dtdf/dt

df/dtdf/dt

df/dt

1 voltage to external free program- free program- free program- free program- free program-

blocking input is mable mable mable mable mable

applied

2 blocking input is released released released after released after released after

released instantaneously instantaneously 1 s 5 s 5 s

3 supply voltage is blocked for blocked for blocked for 1 s blocked for 1 s blocked for 1 s

switched on 200 ms 200 ms

4 3ph measuring volt. released released blocked for 1 s blocked for 5 s blocked for 5 s

is suddenly applied

5 one or several released released blocked blocked blocked

measuring voltages

are switched off

suddenly (phase

failure)

6 measuring voltage released released blocked blocked blocked

smaller UB< (adjust-

able voltage thresh-

old value)

Table 4.1: Dynamic behaviour of MRN3 functionsable 4.1: Dynamic behaviour of MRN3 functions

able 4.1: Dynamic behaviour of MRN3 functionsable 4.1: Dynamic behaviour of MRN3 functions

able 4.1: Dynamic behaviour of MRN3 functions

short circuit protection e.g. able to detect di/dt, the

alternators might be switched off unselectively by the

generator C.B., which is not desireable because the power

supply for the station is endangered and later on

synchronized changeover to the mains is only possible

after manual reset of the overcurrent protection.

To avoid such a situation, the alternator C.B.s must have

a delayed short circuit protection. The time delay must be

long enough so that mains decoupling by the vector surge

relay is guaranteed.

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