Mga Pregunta sa Enterview sa Proteksyon

1). Ano ang gamit ng negative phase sequence relay?

Ang mga negative sequence relays ay nagpoprotekta sa mga generator ug motors gikan sa imbalanced loading nga maaaring resulta gikan sa phase-to-phase faults.

2). Ano ang operating principle sa differential relay?

Ang phasor difference sa duha (o) daghan pa nga similar electrical variables kinahanglan mosobra sa ispesipikong threshold aron mobuo ang differential relay.

3). Asa nimo pipili ang distance protection isip primary protection para sa transmission lines kaysa sa overcurrent protection?

Para sa safety sa transmission lines, mas maayo ang distance relay kay sa over current protection. Ang ilang mga factors kasama na

• Mas quick na protection,

• Mas easy na coordination,

• Mas simple na application,

permanent settings nga dili na gibag-o, reduced impact sa generation level ug fault levels, fault current size, ug ability to support heavy line loading.

4). Ano ang advantages sa biased differential protection kaysa sa differential protection?

Girekomenda ang biased differential relays tungod sa walay effect sa ilang operation ang problema resulta sa variation sa CTs ratios para sa high external short-circuit current values.

5). Asa gigamit ang impedance relays, reactance relays, ug mho relays?

• Ang impedance relay ay appropriate para sa relaying phase faults sa medium-length lines.

• Para sa ground failures, gigamit ang reactance type relays.

• Ang mho type relays ay applicable para sa lengthy transmission lines, lalo na asa mahimong mag occur ang synchronising power surges.

6). Ano ang percentage differential relay?

Ito usa ka differential relay nga ang operational current nga required to trip stated as a percentage of the load current.

7). Ano ang mga types of problems nga mao ang likely to arise during the functioning of a three-phase induction motor?

Ang sumala nga faults mao ang likely to occur sa 3-phase induction motor operation:

• Stator faults

• Phase to phase faults,

• Phase to earth faults, ug

• Inter turn faults,

• Rotor faults

• Earth faults ug

• Inter turn faults

• Prolonged overloading,

• Stalling,

• Unbalanced system voltages,

• Single phasing,

• Under voltage, ug

• Reverse phase.

8). Asa importante ang long-term overload protection para sa induction motors?

Ang prolonged overloading sa induction motor result in excess increases sa temperature sa stator & rotor windings, uban sa damage sa insulation, result in a winding defect. Taliwala, overload protection is provided subject to the motor’s size or rating. Overload protection for motor cannot be initiated during motor startup.

Thermal overload relays (or) inverse over current relays are used to protect motors from extended overloading.

9). Asa may negative sequence current protection ang induction motor?

Kung imbalanced supply voltage ang gihatag sa motor, ang negative sequence of currents flow into it. Ang flow sa negative sequence currents will result in the motor to overheat.

10). Ano ang stalling sa induction motor & paunsa ni siya i-avoid?

Induction motors fail to start owing to technical problems in the motor (or) severe overloading at startup.

Stalling is a condition in which the motor fails to start and is undesirable since the motor draws high currents. As a result, the motor should be disconnected from the power source immediately.

An instantaneous over-current relay is used for protecting the motor from stalling.

11). Ano ang single phasing?

Single phasing sa induction motor is an open circuit in one of the supply lines from a three-phase system. Sa kondisyon kini, ang motor continues to run while supplying a load that does not exceed 57.7% of its normal rating and experiencing the same temperature increase as a three-phase supply operating at full load.

12). Ano ang difficulties na gipasabot sa single phasing sa induction motors?

Single phasing has a number of disadvantages, including

• The potential for severe magnetic unbalance,

• A decrease in motor performance, ug

• Overheating owing to the negative phase sequence currents.

It is not suggested to operate the motor in such a condition since it will harm it. As a result, thermal overload relays can be used to protect the motor against single phasing.

13). Ano ang purpose sa circuit breaker?

An electrical circuit can be closed or opened using a mechanical mechanism called a circuit breaker, depending on normal or abnormal conditions.

14). Ano ang difference sa circuit breaker ug switch?

A switch is basically a device that, when used normally, can open and close a circuit. On the other end, a circuit breaker has the capacity to open & close the contacts in abnormal or fault conditions.

Circuit breakers therefore have a probability to break & generate strong short circuit currents. The circuit beaker’s auto-reclosures have the capacity to reclose after a certain amount of time to check if the short circuit has been resolved.

15). Ano ang “making capacity of circuit breaker” refer to?

The maximum current wave’s peak value (including the DC component) in the initial cycle of the current after the circuit breaker closes the circuit determines the circuit breaker’s making capability during a short circuit.

16). Asa di frequent ang current chopping sa oil circuit breakers?

In most oil circuit breakers, the arc extinguishing power is directly proportional to the size of the current to be interrupted, hence current chopping is uncommon.

17). Ano ang materials sa contacts sa vacuum circuit breakers?

There are several alloys used as contact materials in vacuum circuit breakers, including

• Copper-bismuth,

• Copper-lead,

• Copper-tellurium,

• Silver-bismuth,

• Silver-lead, ug

• Silver-tellurium.

18). Asa consider as a major fault ang current chopping sa circuit breaker?