Quiz - Substation Engineering

Phasors rotate clockwise and counter clockwise. Add the phase shifts due to transformer winding connections. How do you parallel or synchronize two separate system with these variations? Go through this quiz to learn phasing concept.

Transformer phasing quiz

Think you have this covered? This should be a piece of cake.

Does this nameplate convey which way the vectors rotate A-B-C or C-B-A?

Yes

The vectors on this nameplate show the phase shift within the transformer, not how the source vectors are rotating.

Which way are the vectors rotating in 1 and 2?

1: C-B-A 2: A-B-C

1: A-C-B 2: B-A-C

1: A-B-C 2: A-B-C

1 is rotating C-B-A or A-C-B or B-A-C.

2 is rotating A-B-C or B-C-A or C-A-B.

1 is rotating C-B-A or A-C-B or B-A-C.

2 is rotating A-B-C or B-C-A or C-A-B.

It is time to replace a transformer. The old transformer's phase shift is shown in the image. The new one has Dyn1 or Dab 30degree shift.

If you were to parallel this new transformer with other existing transformers (all with Dyn1 or Dab phase shift), how would you land the phase conductors on the bushings? (Hint: use the infographic in the article)

Cph on H1 and X1 | Bph on H2 and X2 | Aph on H3 and X3

Aph on H1 and X1 | Bph on H2 and X2 | Cph on H3 and X3

Bph on H1 and X1 | Aph on H2 and X2 | Cph on H3 and X3

The source rotation is A-B-C. The new transformers phase shift is the same as the old one. Therefore we keep the old pattern: Aph on H1 and X1 | Bph on H2 and X2 | Cph on H3 and X3.

Follow this infographic (on this blog) to make sense of this.

The source rotation is A-B-C. The new transformers phase shift is the same as the old one. Therefore we keep the old pattern: Aph on H1 and X1 | Bph on H2 and X2 | Cph on H3 and X3.

Follow this infographic (on this blog) to make sense of this.

Consider this scenario, if the new transformer has Dyn11 or Dac phase shift, how would you land the phases now?

Cph on H1 and X1 | Aph on H2 and X2 | Bph on H3 and X3

Aph on H1 and X1 | Bph on H2 and X2 | Cph on H3 and X3

Cph on H1 and X1 | Bph on H2 and X2 | Aph on H3 and X3

The source rotation is A-B-C. The new transformers phase shift is NOT the same as old one. Therefore we flip the phases: Cph on H1 and X1 | Bph on H2 and X2 | Aph on H3 and X3.

Follow this infographic (on this blog) to make sense of this.

The source rotation is A-B-C. The new transformers phase shift is NOT the same as old one. Therefore we flip the phases: Cph on H1 and X1 | Bph on H2 and X2 | Aph on H3 and X3.

Follow this infographic (on this blog) to make sense of this.

Your score is

The average score is 45%

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Different pieces of equipment makeup a substation. Some of them are obvious, like a breaker and a transformer. With this quiz, dive a little deeper to understand some of the intricacies with equipment application.

Substation Major Equipment

It's simple, let's begin.

In a distribution substation, the available ground-fault current on the low side of the step-down transformer is excessive, over-dutying the switching equipment. What is your cost-effective solution to reducing the fault current?

Add current limiting fuses in series on the switchgear

Buy new transformer with higher impedance (%Z)

Add series inductors

Add inductor in the transformer neutral

All methods mentioned help with limiting the fault current. The cheapest though is a neutral inductor, especially when mounted directly on the transformer. Learn more.

Current limiting fuses directly on the transformer secondary are rare. Mostly because of the continuous current requirement (1000amps or more) - fuses are rarely fabricated this large. This was a trap answer.

All methods mentioned help with limiting the fault current. The cheapest though is a neutral inductor, especially when mounted directly on the transformer. Learn more.

For which event should a surge arrester operate? Check all that apply.

Temporary overvoltage

Phase-to-ground short-circuit

Switching surge

Lightning strike

Surge arresters are specified to discharge lightning strikes and switching surges. The equipment/system insulation can handle temporary overvoltage. Learn more.

You are building an interconnect station, tying wind farm generation to the power grid. At the substation, the sources are tied through a tie-breaker. Which device would you install to make sure the sources are synchronized?

Current transformer

Power transformer

Voltage transformer

Ideal transformer

A synchronization check is done using a relay. It needs low voltage input (from both sides), obtained using a voltage transformer a.k.a. instrument transformer. Learn more.

A transformer develops an internal fault. Which device would you install on the transformer high-side to interrupt fault current?

Disconnect switch

Circuit breaker

Circuit switcher

Either a breaker or a circuit switcher

Both the breaker and the switcher have an interrupting chamber that can safely interrupt the fault current. A switch does not. A switch will draw an arc, that is damaging and a safety hazard. Learn more about switches here and circuit switchers here.

Which combination of devices would you use to implement power line carrier?

Wave trap, capacitor voltage transformer and line tuner

Wave trap and line tuner

Wavetrap, capacitor coupled voltage transformer, and line tuner

You need a device that allows a certain frequency to pass (CCVT and line tuner) and a device that stops it (wavetrap). Note a capacitor voltage transformer does not come with coupling accessories as such it does not work for transmitting carrier frequencies.

Click here for more detail on wavetrap and here for CCVT.

What's the purpose of a conventional power transformer?

Transform voltage only

Transform power, voltage, and current

Transform voltage and current

Transforms voltage and current only. Power remains the same on both sides. Learn more.

An industrial facility is plagued with voltage flicker (due to harmonics) and poor power factor at the service entrance. Which device would you install to fix both issues?

Voltage regulator

Harmonic filter bank

Install capacitor bank

Cap bank fixes the poor power factor only. It does provide a low impedance path for harmonics but it is not tuned to filter them out. A regulator does not remove the harmonics and neither does it fix the power factor. A filter bank addresses both - it is made up of inductors and capacitors therefore tunable and also capable of releasing VARs. (Note: one manifestation of harmonics is voltage flicker). Learn more.

Your score is

The average score is 42%

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Transmitting a direct transfer trip signal depends on certain requirements, for instance substation layout, location of fault, etc. Learn when to initiate a DTT and when not to, take the quiz.

Direct Transfer Trip Quiz

Get ready to learn this topic like never before.

For a transformer fault at substation 2, would you transmit DTT to substation 1?

Yes

Incorrect.

Fault current contribution from substation 1 can be stopped by tripping 2CB1. DTT transmission to Substation 1 not required.

Correct

Fault current contribution from substation 1 can be stopped by tripping 2CB1. DTT transmission to Substation 1 not required.

For a fault on Bus 1, would you implement a direct transfer trip (pilot) scheme to trip breakers tied to the same bus?

Yes

Incorrect.

All breakers shown are within the substation. You can wire the trip 'a' contact from a lockout relay to breaker's trip coil physically. Therefore DTT scheme is not required.

Correct.

All breakers shown are within the substation. You can wire the trip 'a' contact from a lockout relay to breaker's trip coil physically. Therefore DTT scheme is not required.

For a temporary fault on the transmission line, would you transmit DTT from either one substation?

Maybe

Yes

Incorrect.

Faults on the transmission line are usually temporary. Line protection relays require time to implement its reclosing logic. DTT is not initiated.

Note that designing the protection system is an art and not an exact science. How the relay engineer "paints" differs from utility to utility. For instance, certain t-lines pass through a dense forest while others through an arid desert. The utility engineer dealing with the trees (causing higher temporary faults) may choose to go with reclosing logic - no DTT. In the case of the desert, the faults could be interpreted as permanent and whichever relay detects the fault using its Zone 1 elements, transmits DTT to the remote-end substation relay.

Correct.

Faults on the transmission line are usually temporary. Line protection relays require time to implement its reclosing logic. DTT is not initiated.

Note that designing the protection system is an art and not an exact science. How the relay engineer "paints" differs from utility to utility. For instance, certain t-lines pass through dense forest while others through an arid desert. The utility engineer dealing with the trees (causing higher temporary faults) may choose to go with reclosing logic - no DTT. In the case of the desert, the faults could be interpreted as permanent and whichever relay detects the fault using its Zone 1 elements, transmits DTT to the remote-end substation relay.

For what kind of fault at Substation 1 would you transmit a DTT to Substation 2 (to trip breaker 2CB1)?

Transformer T1 failure

Bus 1 fault

1CB1 failure to trip

1CB2 failure to trip

All of the above

Incorrect.

For the fault scenarios listed, there is no way to stop the fault contribution from Substation 2. There is no breaker on the line-exit at Substation 1 (You cannot use a switch to interrupt load or fault current. Learn more). If one existed, tripping it would suffice, and a DTT wouldn't be necessary.

Correct.

Assume circuit breaker 3CB2 fails at substation 3. DTT is transmitted to Substation 2 to trip 2CB1 and 2CB3. Which auxiliary relay would you install at Substation 2 to trip breakers 2CB1 and 2CB3?

86 - Lockout relay

94 - Self-reset tripping relay

Incorrect.

A quick word on 94 and 86.

94 relay - when its operating coil is energized - it trips. When de-energized, it resets automatically.

86 relay - when its operating coil is energized - it trips. When de-energized, it does not reset. Someone needs to be at the substation to reset it.

Considering the severe event did not occur at Substation 2, it makes no sense in installing a lockout at this station and needlessly sending someone to reset it. A 94 relay is used in this scenario. Some utilities may also use microprocessor relays to trip the breaker (instead of a 94 aux relay).

Correct.

A quick word on 94 and 86.

94 relay - when its operating coil is energized - it trips. When de-energized, it resets automatically.

86 relay - when its operating coil is energized - it trips. When de-energized, it does not reset. Someone needs to be at the substation to reset it.

Your score is

The average score is 52%

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Quiz – Substation Engineering

In a distribution substation, the available ground-fault current on the low side of the step-down transformer is excessive, over-dutying the switching equipment. What is your cost-effective solution to reducing the fault current?

For which event should a surge arrester operate? Check all that apply.

You are building an interconnect station, tying wind farm generation to the power grid. At the substation, the sources are tied through a tie-breaker. Which device would you install to make sure the sources are synchronized?

A transformer develops an internal fault. Which device would you install on the transformer high-side to interrupt fault current?

Which combination of devices would you use to implement power line carrier?

What's the purpose of a conventional power transformer?

An industrial facility is plagued with voltage flicker (due to harmonics) and poor power factor at the service entrance. Which device would you install to fix both issues?

For a transformer fault at substation 2, would you transmit DTT to substation 1?

For a fault on Bus 1, would you implement a direct transfer trip (pilot) scheme to trip breakers tied to the same bus?

For a temporary fault on the transmission line, would you transmit DTT from either one substation?

For what kind of fault at Substation 1 would you transmit a DTT to Substation 2 (to trip breaker 2CB1)?

Assume circuit breaker 3CB2 fails at substation 3. DTT is transmitted to Substation 2 to trip 2CB1 and 2CB3. Which auxiliary relay would you install at Substation 2 to trip breakers 2CB1 and 2CB3?

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