1). What is meant by “Synchronous Condenser”?
Synchronous condenser refers to an over-excited synchronous motor that is running without a load. It improves the system’s power factor.
2). What is Electrical Traction?
Electric traction means the use of electric power to drive traction which are applied to locomotives.
3). What is “pu” in electrical engineering?
Pu refers to per unit. This is used in a single-line diagram of the power distribution. Power distribution is a complex electrical circuit with multiple components (generators, transformers, and loads) with varying ratings (MVA and KV).
To standardize ratings, we employ the pu principle, where the component’s highest MVA & KV ratings are regarded the base values.
4). Can you describe the operations carried out in the thermal power stations?
Water is boiled in boiler with help of coal. This generates steam allowing steam to pass through the turbine causes it to rotate. The turbine is connected to a generator. Mechanical energy of the turbine is then converted into electrical energy with the help of the generator.
5). What is ACSR cable & where do we utilize it?
ACSR – Aluminium Conductor Steel Reinforced
ACSR conductor is utilized in transmission and distribution.
6). Why are synchronous generators employed in the generation of electrical power?
Synchronous machines can function under a wide range of power factors. Synchronous generators produce energy.
7). Why do we utilize vacuum circuit breakers in high transmission systems rather than air circuit breakers?
Vacuum has a higher arc quenching characteristic than air. The dielectric strength of vacuum is eight times that of air.
As a result, high voltage lines employ vacuum circuit breakers, while low voltage lines use air circuit breakers.
8). What is the difference between a surge arrestor and a lightning arrestor?
Lightning arrestor is mounted outside to ground the influence of lightning, while a surge arrestor is installed inside panels with resistors to consume energy and eliminate the effect of surges.
9). Explain the working principle of the circuit breaker
A circuit breaker is one that builds (or) interrupts a circuit.
It has two contacts:
- Fixed Contact and
- Movable Contact.
Normally, the moving contact makes contact with the stationary contact, establishing a closed circuit that allows current to flow.
During abnormal and fault conditions (i.e. current > rated value), the relay detects the faults & signals the circuit breaker.
The circuit breaker’s moving contact separates from the fixed contact, creating an arc and forming an open circuit.
Arcs are extinguished using medium such as
- Air,
- Oil,
- Vacuum, and
- SF6 gas.
10). What is power factor? Should it be higher or lower? why?
The power factor is the ratio of the actual power to the apparent power. It should preferably be 1.
- If it is too low, cable overheating and equipment overload can result.
- If it is more than 1, the load will function as a capacitor, feeding the source & causing tripping.
- (If pf is weak, such as 0.17, to achieve actual power, the load must draw higher current (V constant), resulting in higher losses.
- If pf is good, for example 0.95, the load must draw less current (V constant), resulting in lower losses.
11). What distinguishes a circuit breaker from an isolator?
An isolator is a device that separates downstream and upstream circuits for maintenance purposes.
It is manually operated & does not have a solenoid, unlike a circuit breaker.
It must not be utilized while under load. Its categorization is depends on rated current.
Circuit breakers are automatic devices that break circuits during abnormal conditions such as short circuits (or) overloads.
They have three specifications.
- Rated current
- Short circuit breaking capacity, &
- Instantaneous tripping current.
12). What is a Buchholz Relay and how does it affect the transformer?
A Buchholz relay is a gas-based relay designed intended to protect a transformer against internal issues. When an internal fault arises in a transformer, the Buchholz relay will sound an alarm for a short period of time.
If the transformer is disconnected from the circuit, the sound will stop. Otherwise, the relay will trip the circuit using its own mechanism.
13). What is the Ferranti Effect?
When the receiving end voltage exceeds the sending end voltage is called Ferranti Effect
14). Explain the different types of earthing
There are two types of earthing:
- Equipment earthing and
- System earthing.
Equipment Earthing: it’s important to earth the non-conducting parts to protect human safety.
System Earthing: System Earthing involves grounding the neutral of supply source (e.g., transformer or generator).
This prevents imbalanced loading from causing unbalanced voltages by not shifting the neutral. We can also protect the equipment.
System Earthing are further classified into 3 types:
- Direct earthing,
- Impedance earthing, and
- Resistive earthing.
15). What is the difference between MCB and MCCB, and where can they be used?
MCBs are miniature circuit breakers designed for thermal operation on overload current and magnetic operation on short circuit current. It is available in a small current rating.
MCCBs are molded case circuit breakers that work thermally for overload and magnetically for the short circuit protection.
Under-voltage and under-frequency may be built-in.
Normally, it is utilized where the normal current exceeds 100 A.
16). Where should lighting arrestors be installed in distribution lines?
Near
- Distribution Transformers,
- 11kv Outgoing Feeders,
- 33kv Incoming Feeders, and
- Power Transformers at Substations.
17). How would you define IDMT relay?
IDMT Relay – Inverse Definite Minimum Time Relay
The tripping time reduces as the amplitude of the fault current increases (inversely proportional to each other).
18). What is derating?
The current currying of the cables varies based on site temperature, kind of run (duct, trench, buried), tray number, trench depth, and cable distance.
Derating occurs when the real current currying capacity of a cable falls below the current currying capacity stated in the cable catalogue.
19). What is the difference between an overvoltage relay and an overcurrent relay?
The current increases not only for over-voltages, but also for under-voltages (since most loads are nonlinear).
As a result, overvoltage and overcurrent protection are fundamentally different.
The overvoltage relay detects over-voltages and protects the system from the insulation breakdown and firing.
Overcurrent relays detect internal short circuits, overloads, and ground faults to prevent system failure and fires.
Improve system security.
It should feature both overvoltage and overcurrent relays.
20). What is a Reverse Power Relay?
Reverse power relays are utilized to prevent power flowing from the grid to generator.
If the generating units are turned off, the plant may draw power from the grid.
21). What type of motor is utilized in trains & what is the supply rating?
DC series motor is utilized in trains for its high starting torque, and the operating voltage rating is 1500V DC.
22). What is meant by Sag?
Sag refers to the difference in levels between support points and the conductor’s lowest point.
23). What is corona?
Corona is the violet color glow, hissing noise, and the generation of ozone gas created by an overhead transmission line.
24). How can we lessen the effects of corona?
Increasing conductor size reduces corona effects by raising the voltage at which they occur.
To eliminate corona effects, increase conductor spacing to boost the voltage at which it occurs.
25). What is tariff?
Tariff refers to the rate at which electrical energy is given to a consumer.
The tariff should consist of the following things such as:
- Recovering the cost of generating power in the electrical power station.
- Recovering capital expenditure in transmission & distribution infrastructure.
- Recover operational and supply costs.
- Make a reasonable profit on capital expenditure.
