B3 4.2

Faults must be minimized or cleared to:

A∅            X             A∅

When B∅ circuit comes into contact with the A∅ or C∅ circuit

When one of the phases comes into contact with ground

In order to maintain Power System stability and continuity of customer service, some form of                  is needed

What are the most common devices designed to detect fault current and isolate fault

Combine the function of fault detection and circuit clearing in one device

Characteristics of fuses

Fuses are best suited for                where they do not operate in conjunction with other protective devices

In the                 fuse the complete fuse assembly must be
replaced each time it blows

The                  fuse is constructed so the casing can be easily dismantled and the blown link can be replaced with a new fuse link of proper amperage and voltage ratings

Non-current limiting fuse, with the link contained in an explosion chamber - used in Station Service

The                is a non current-limiting fuse which consists of a glass tube, a fuse element and an arc extinguishing liquid

The fuse element is surrounded by a tube liner of compressed boric acid

Fuses used extensively for service with potential transformers and control power transformers.

                are normally used in underground distribution circuits where voltages do not exceed
15kV

                  is one in which the breaker is tripped by direct mechanical action when the current reaches a pre-determined value

Direct acting trips and fuses can only be employed for              protection

True/ False

Relays can be used to protect against undervoltage,
overvoltage, unbalanced phases, low frequency, current differential, and phase angle comparison
True False

Measuring instruments equipped with auxiliary contacts
that operate when the quantities flowing through them either exceeds or drops below a predetermined value

True/False

Relays may not be used to locate a fault by measuring the
line impedance (distance) from the relay to the fault
True False

Used where an instantaneous operation is required in a relay with an adjustable pick-up.

A relay that consist of a disc positioned between two magnetic poles that is not instantaneous

A relay does three things in order to accomplish its purpose. It must:

A relay does three things in order to accomplish its purpose. It must

True/False

The sense function in a relay input circuit. If the input circuit is connected to a source of voltage or current, the relay is monitoring an electrical quantity.
True False

The                 function of a relay, is accomplished by mechanisms within the relay (relay movement). This mechanism is adjusted to respond to a specific level or degree of input

The                function is done by closing relay output contacts that most often are used to open or trip circuit breakers

What the four basic characteristics of relay

A device located under the bushing, with the primary side  connected to the source to be monitored and the secondary side is connected to the relay circuit

Reduce bus or line voltage to 120 volts.

A short in the                circuit may prevent the relay from seeing the fault

A DC short in the relay circuit may cause a to               blow

                are installed in the positive side of the DC to allow relays to be manually blocked

True/False

The Circuit Breaker status signals, and the Relay Trip Circuit, are made up through pallet switches, known as the A & B
pallets for the circuit breaker
True False

                 is used in system protection schemes to monitor relay tripping frequency signals

Carrier Equipment includes such items as:

Provides the path for the terminals of a monitored
line section to communicate, The two most common methods used by the Department are to transmit an audio-frequency tone over a leased telephone line or use the line itself

True/False

Wave Trap filters the audio-frequency tone, thus preventing the
carrier signal from going beyond the circuit is it monitoring
True False

Used in Receiving Stations (RS) for transmission and sub-transmission line protection and as back-up protection on banks in Substations

True/False

When overcurrent relays are used to protect lines, only the Receiving Station end of the line will be tripped by the relay
True False

When overcurrent relays are used to protect banks, normally
only the bank                  will trip

                  overcurrent relays have no intentional time delay, they are used for tripping when extremely high current values are present

                overcurrent relays have a time delay element, the time delay is needed so that tripping can be coordinated with other relays or fuses.

Protects lines in Distributing Stations, Trips only the local end of the faulted line

True/False

Directional overcurrent uses an overcurrent relay with a directional element that requires both current and voltage
True False

Protects, a particular piece of equipment such as, a
transformer, condenser, generator, or bus Trips all sources and loads to the faulted circuit.

True/False

Sudden pressure relays are commonly used to protect transformers
True False

One of the most common sudden pressure relays used on the Power System is the               relay

                   compare the voltage or current on both sides of the equipment being protected

                   is a back-up protection used to clear a fault if a circuit breaker fails to trip

What of relay trips the bank low side circuit breakers when the frequency drops below a predetermined value

True/False

Under-frequency relays are used at most receiving and switching stations.
True False

True/False

Bank low side circuit breakers trip on under-frequency. The load is dropped, but the Transmission System and Station Service are maintained.
True False

                        protects capacitors and trips the capacitor source CB

Protects Transmissions lines and trips both ends of the faulted line

True/False

Distance relays are directional, which means they look in only one direction for a fault
True False

When a fault occurs a long distance away, the bus current increase is                than when the fault is close in. Conversely, when the fault is a long distance away the bus voltage                 will be less than when the fault is close in.

True/False

Distance relays are not designed to operate on line to ground faults because the impedance changes constantly
True False

True/Fasle

The impedance of a transmission line depends on
the length of the line
the size of the conductor
the material used to make the conductor
the spacing between conductors
the height above ground
True False

True/False

Phase comparison relays are similar to differential or pilot wire relays, phase comparison relays compare the phase angle and current magnitude of the line at each terminal
True False

True/False

If a receiver stops getting the Guard Frequency without immediately receiving a trip frequency, a "loss of guard" or "transfer trip signal" alarm is initiated
True False

What are the transfer trip relays used by DWP

In this method, the relays are set to protect 80 to 90% of the line. If a fault is detected, a trip signal is sent to the local circuit breaker and the transmitter sends a trip signal to the remote end.

The transfer trip signal and               must be received simultaneously to initiate a remote trip

This method of transfer trip protection uses directionally controlled relays set to overreach the remote terminal.

Relays that operate in order to assist another relays or devices

Once the auxiliary relay is energized by the protective relay, it is                 .

The general philosophy of relay application is to divide the power system into                  .

True/False

The Screw-Base Plug fuse and the Cartridge fuse. The Cartridge fuse is the type most often used by the Department.
True False

Why must the CTs must never be energized with the secondary open