Sub Transmission Protection Relay

Introduction:

Due to the increase of demand in the power network and preventing of excess shutdown time and malfunction of protective equipment, followed by the spread of accidents on the above network's distribution and prevention of damage to equipment. it is necessary to review protection relays in the transmission and distribution sectors.in this article, Minimum protection relays required and how to adjust these relays for sub-transmission has been determined and proposed.

Required Protection:

1- 20kv Feeder Protection

· Over-Current (OC).

· Earth-Fault (EF).

· Sensitive-Earth-Fault (SEF).

For SEF Relays, Be Sure to Use C.T with Balancing Core.

2- Capacitor Feeder Protection

· Over-Current (OC).

· Under-Current (UC).

· Var-Control-Regulator (VCR).

· Earth-Fault. (EF)

· Unbalance Current and Voltage.

In the Event of An Error on The Output Feeders, The Capacitive Bank May Feed the Reactive Fault Current, In Which Case It Is Necessary to Select the OC And EF Relays in A Directional Direction.

3- Distributed Generation Feeder Protection

· Over-Current (OC).

· Earth-Fault (EF).

Both Are Directed and Preferably Two-Way.

4- 20kv Protection Coupling

· Over-Current (OC).

· Earth-Fault (EF).

· Zero-Voltage (ZV).

· Over-Voltage (OV).

· Under-Voltage (UV).

The OC, EF Relay Settings Must Be Synchronized with The Output Feeder Relays and The Incoming Transformer Relays.

5- Transformer Incoming Protection 20KV,30KV

· Over-Current (OC).

· Earth-Fault (EF).

· Neutral Earth Fault (NEF)

· Sensitive-Earth-Fault (SEF).

NEF Relay Is Necessary for Ground Transformer.

6- Power Transformer Protection.

Main Protection:

· Differential.

· Limited Ground Connection Relay in High/Low Voltage (REF).

Supportive Protection:

· Over-Current (OC).

· Earth-Fault (EF).

In Addition, The Main Protections and Supports Should Be Considered as Separate Relays.

7- Protection of The Coupling Switch (63KV-132KV).

· Over-Current (OC).

· Earth-Fault (EF).

8- Protection of Busbar (63KV-132KV).

If the Number of Feeders for High Voltage Lines and Transient Feeders Is More Than 8, The Feeder Busbar Protection Will Be Required.

In H Substation, Using Is Not Necessary to Have Busbar Protection.

9- Line Entry Feeder Protection

Main Protection:

· Distance Relay for Long Lines.

· Differential Relay for Short Lines.

Backup protection:

· Over-Current (OC).

· Earth-Fault (EF).

Adjusting protection relay:

20KV output protection feeders:

Adjustment over current relay OC:

The following information is required to adjust the relay current:

1)     Nominal current and CT ratio.

2)     Nominal heat tolerable rated current of 20 kV.

3)     Minimum current output loader loaded by the distribution.

4)     Maximum output current loading current.

5)     Short circuit current at the beginning of the feeder.

6)     Short circuit current at the end of the feeder.

The value of the overcurrent relay setting should be considered according to the above:

120% × I load max < Is < In – thermal

 120% × I load max < Is < In -ct

The coefficient is 120% due to the tolerance of multiple values in the current measured by the relay.

Is> I -n C.T error (5%In) +Relay error(5%In) +I?V (10%In).

Is: The amount of current regulation.

In: I n-thermal or I n-CT whichever was smaller.

I n-thermal thermal nominal current that line can tolerate.

In-CT: Nominal current of the ct-In current transformer.

I load max: Maximum loading current of the output feeder.

I?V: Voltage changes due to voltage changes.

- In the case of the instantaneous unit, its setting is 5 to 10 times that of the Current setting Is considered.

 - Where an adjustment is based on fault current near busbars such as sensitive Industrial load and bing auto recloser is on transmission line….. the setting of the instantaneous unit is as follows:

I inst = 90% Is.c.

I sc: Error flow on 20 kV busbar.

Time setting:

The time setting of the OC relay either as a specific time or as a reverse time (basically the short-circuit three-phase connection is performed at the beginning of the output feeder) and is considered in such a way that the three-phase fault at the beginning of the output feeder is equivalent to the three-phase fault on the 20 kV busbar in the shortest time. it is possible (about 200 milliseconds) to disconnect.

Therefore, the TMS value is determined according to this point:

TMS → Topr  ≈  200 msec

Adjustment Earth Fault Relay EF:

Current setting:

Depending on how the earthing system, we will have:

1-Systems that are directly grounded.

In these systems, the adjustment current must be less than the minimum short-circuit current at the end of the output feeder so that the relay can detect it and greater than 5% of the rated current CT or the rated output current of the output feeder, whichever is smaller.

Isc 1ph> Iset> 5% In-ct  or In-thermal

If the load imbalance is more than 5-10% In-ct, the adjustment value is equal to

Iset = 20-30% In-ct

2- Systems that are grounded with high impedance.

Iset > 30% (In-c.t or In-thermal) each one was smaller.

Also, I set should be considered less than the continuous allowable current of the ground

 If the S.E.F relay does not exist, the setup value is as follows:

I set > 10% (In-CT or In-thermal)                        (Each one was smaller)

The characteristic curve is usually N-I. For special cases especially the possibility of harmony

With downstream protection in distribution with N-I curve, V-I or E-I is used.

Instant setup: From the following relationships

I set =70-80% In-GT

I set = (5-10) Iset-EF

Whichever was smaller was chosen.

I n-GT = Name of a ground transformer

I set-EF = EF relay current setting value

Time setting:

Like the time setting, the OC relay is considered

TMS → T opr ≈ 200 msec

For short-circuit single-phase connection at the beginning of the 20 kV output feeder.

Current setting:

Initial current,

I set=4-10A

Time setting:

T trip=3-10 sec

Capacitor feeder protection:

Adjusting OC

Current Setting:

I set> (120% In)

In: Nominal current of the capacitor bank.

Time setting:

TMS→  T opr ≈ 200 msec

Curve type: Perform as OC output feeders.

 Instantaneous OC relay unit should be out of circuit due to the presence of capacitor leakage current.

Earth Fault relay adjusting(EF):

Current Unit Adjusting:

I set> (10-20% In) (Capacitor Bank)

Time setting:

Ts< T (Maximum tolerance for short capacitor connection)

Curve type: Like EF output feeders.

The instantaneous unit outside the circuit.

Over Current Relay:

V set=120 %Un

T set =3 sec

Zero Voltage relay:(with busbar 20 KV)

V set=50 %Un

T set =4 sec

Unbalance current relay:

I set= 70% In

In = rated current of a capacitor cell.

T set =5 sec

Unbalance voltage relay:

V set =3 V

 PT ratio is usually 6000V/100V

T=5 sec

Under Current Relay:

I set < Capacitor transit current per symmetrical cell removal from all three phases

T=60 sec

How to set 20 kV bus coupler protection relays:

Over Current Relay:

I set= % 120 (Transformer Nominal current in low voltage)

TMS the operating time should be 0.2-0.4 seconds longer than the output feeder relay time.

and 0.2-0.4 seconds less than the incoming relay time.

Earth Fault relay (EF):

I set=10- % In

In: Transformer nominal current in low voltage.

TMS → OC relay

Curve type: Selects as OC relay.

The immediate protection unit of the Bus coupler will be out of the circuit (both OC and EF). It should be noted that these current settings are for both modes of power with powers. Equalize and adjust if two transformers with different powers are parallel. A current based on the power (nominal current) of the transformer is less capacious.

Adjusting the keys of the Incoming protection relay 20 KV.

Over Current Relay:

I set= % 120 (Transformer Nominal current in low voltage)

TMS the operating time should be 0.2-0.4 seconds longer than OC relay in output bus coupler.

Earth Fault relay (EF):

I set=10-30 % In

TMS the operating time should be 0.2-0.4 seconds longer than EF relay in bus coupler.

In high voltage substation where that lines do not have a power switch, if used the C.O.D. directional current relay in incoming transformer, adjusted as follows:

Iset = 250 A

MTA= -45 '(Maximum Torque Angle)

T.M.S = 0.1 , Curve : S.I. (Standard Inverse or Normally Inverse)

Power transformer OC and EF relays adjustment:

The over-current relay in High Voltage:

Current setting:

I set=120 % In(Nominal transformer current)

Time setting:

TMS should be matched with OC relay operating time so that 0.2-0.3 seconds is more than the OC relay performance in the LV side.

Earth Faulting in High Voltage:

Current setting:

If(min)/3 > IS > 20 % In

The minimum shot circuit current in phase-to-ground connection at the end of the sub-transmission line and the coefficient is 1/3 Due to the maximum strength of the connecting arc.

TMS is calculated according to the following:

1-     The operating time of the EF relay line is considered for If1ph(max) and the value of 0.4-0.3 seconds is added to this time and we calculate the TMS value for the EF relay on the HV side of the transformer.

2-     Approximately consider the operating time T=1 sec for If1P(max).

Sub transmission line protection OC and EF:

Adjusting OC relay in sub-transmission:

Current setting:

Iset=120%Inct or I thermal

Time setting:

Toper=Tz2+0.3 sec

Adjusting EF relay in sub-transmission:

Current setting:

Iset=20%Inct or I thermal

Time setting:

The TMS setting is similar to the OC relay.

Adjusting the differential relay of the power transformer in sub-transmission:

Current setting:

Iset (Diff) > CT Error (2x5%) + CT mismatch error + Tap changer error (10%) + Relay error (1%) + margin (5%)

Adjust Slop:

Slope 1 = (25-35) %

Slope2= (50-60) %

Instantaneous unit setting:

2 nd Harmonic: (15-20) % In

5 th Harmonic:30%In

Adjusting Low Impedance R.E.F relay:

Current setting:

I set> CT error (5%) +Relay error (1-5%) +margin (5%)

Adjust Slop:

Slope setting is considered as Slope = 0%, so the usual setting for slope is considered to be 0%.

Adjusting high Impedance R.E.F relay:

VR= (Rct+2Rcable)*IF/N

VR- Double relay voltage and stable resistance.

RCT - Important resistance of secondary CT coil.

R cable - Important resistance of current cables.

IF - Error flow.

N - CT conversion ratio.

Therefore, the stabilizing resistance is calculated as follows:

R stabilizer> (VR /I setting) – Rrelay

We use the following relation to select metrosil.

I metrosil=1000X

V metrosil= 0.84 * C*

The values of B and C are methyl properties.

Adjusting AVR relay:

Vs = 1.02

 ?Vs = 1.5 %

 T1 = 80 sec

 T2 = 40 sec

Adjust Distance Relay:

Zone 1 setting:

Z1=80-85%ZL1

Z1 = zone 1 impedance.

ZL1 = Impedance Protected Line.

Zone 2 setting: In general, the following are considered:

In determining the range of zone 2, the distance relay must be considered under two conditions:

A: The second area of the distillery relay must see the shin around it.

B: The second area of the distance relay the protected line should not be the shortest with the second area of the distance relay.

The next line is performance interference.

Therefore, zone 2 adjustment is generally considered as follows:

The second range: at least 120% of the impedance of the protected line, provided that the total 100% impedance of the protected line plus 50% impedance of the shortest next line don't be bigger.

Z2 = 120% ZL1 & Z2 < (100%ZL1 + 50% Zn.s.l)

Zn.s.l = Impedance is the shortest next line.

Tz2=400-500 msec

Z3=100%Zl+120%Zn.l.l

Zn.l.l = Impedance is the shortest next line.

T z3 = 800-1000 msec

Set the Reveres zone:

ZRevers=20-30%Z1

TReverse=1200 msec

Impedance starter (Non-directional Zone):

20% more than last zoon    T=2.2-2.4 sec

Determine the direction of resistance for the distance relay:

To do this, consider the minimum impedance resistance (R load min) of the load and the zone resistance limit

? R 3G – R 4G = 80% R load min

? R 3ph – R 4ph = 60% R load min

? R 2G = 0.8 R 3G – R 4G

? R 2ph = 0.8 R 3ph – R 4ph

? R 1G = 0.8 R 2G

? R 1ph = 0.8 R 2ph

For Encroachment Load relays, see the last resistance zone (zone 3 or 4) attention to the maximum value specified X / R is determined by the relay manufacturer and for zones 2 and 1 of The following relationships are used:

? R 2G = 0.8 R 3G – R 4G

? R 2ph = 0.8 R 3ph – R 4ph

? R 1G = 0.8 R 2G

? R 1ph = 0.8 R 2ph

Power Swing Blocking:

This unit must be in offline mode in the above distribution networks that are operated radially. In the above distribution networks, which are used as ringtones, this unit is adjusted according to the manufacturer's instructions.

Switch On To Fault:

This function must be in On mode and the following items must be considered:

? The status of the broker should be considered.

? Active Detection Line Dead status.

? Read the manufacturer's instructions for the relay in question.

Voltage Transformer Fuse Failure VTFF:

The following items should be considered for this unit:

- MCB status of voltage protection in Marshall Box Trans Voltage Transformer

- The adjustment of this unit is done according to the different algorithms used by the manufacturers, taking into account the instructions of the relay manufacturer.

Adjusting Over Voltage Relay:

V set = 115% Un

T = 4 sec

Adjusting Zero Voltage Relay:

V set = 50% Un

T= 4 sec