1). What is the difference between an MCB, MCCB and ACB?
The difference between an MCB, MCCB and ACB
| MCB | MCCB | ACB |
| An MCB is used for low-current protection in small circuits. | An MCCB for greater currents with adjustable settings for industrial feeders. | An ACB as the primary incoming protection device in low-voltage switchgear. |
2). What is the function of a Current Transformer (CT)?
A current transformer (CT) decreases high primary current to a smaller more measurable value allowing for safe metering, protection and control.
3). Why is a Neutral Grounding Resistor (NGR) used?
An NGR is used to reduce earth fault current to a safe level, reducing equipment damage and maintaining system stability during ground disturbances.
4). What is Harmonic Distortion?
- Harmonic distortion is the undesirable higher-frequency components produced by nonlinear loads such as
- VFDs,
- UPS systems, &
- SMPS devices
which can result in overheating and poor power quality.
5). What is the purpose of a Variable Frequency Drive (VFD)?
A Variable Frequency Drive (VFD) adjusts the speed and torque of an alternating current motor by adjusting the supply voltage & also the frequency while reducing the starting current.
6). What is Insulation Resistance (IR) testing?
IR – Insulation Resistance testing assesses insulation status by delivering a high DC voltage across conductors & ground and the low insulation resistance implies insulation breakdown or moisture infiltration.
7). Why is a Star–Delta starter used?
A stardelta starter reduces the starting current of heavy motors by √3 times and minimizes voltage drops in the supply system.
8). What is the function of an Automatic Voltage Regulator (AVR) in a generator?
An AVR adjusts a generator’s excitation current to keep the terminal voltage constant under varying load conditions.
9). What is the difference between LT and HT cables?
LT cables are rated up to 1.1 kV but HT cables are rated higher than 1.1 kV and up to 33 kV with thicker insulation and shielding.
10). Why is Earthing important?
Earthing provides a low-resistance path for the fault current assuring the safety of people, equipment and structures from high voltage.
11). What is the purpose of a Capacitor Bank?
A capacitor bank
- Improves power factor,
- Reduces energy losses,
- Improves system efficiency and
- Avoids utility fines.
12). What are common causes of Motor Overheating?
Motor overheating may be caused by:
- Overloading,
- Phase imbalance,
- Low insulating resistance,
- Poor ventilation,
- Mechanical binding &
- Harmonics of VFDs.
13). What is a Protection Relay?
A protection relay monitors electrical characteristics and automatically disconnects the circuit when abnormal (or) fault conditions.
14). What is the Lockout Tagout (LOTO) procedure?
LOTO is a safety technique that ensures electrical or mechanical equipment is totally disconnected from all energy sources prior to maintenance activities commence.
15). What is the difference between 2-wire, 3-wire and 4-wire systems?
The difference between 2-wire, 3-wire and 4-wire systems are:
| 2-Wire System | 3-Wire System | 4-Wire System |
| A 2-wire system gives power to single-phase loads. | A 3-wire system powers balanced three-phase loads without a neutral. | A 4-wire system powers mixed single-phase & three-phase loads with a neutral. |
16). What is Switchgear?
Switchgear is a collection of
- Electrical disconnects,
- Circuit breakers,
- Busbars and
- Safety devices
used to manage and protect electrical systems.
17). Why is a transformer rated in kVA instead of kW?
A transformer’s kVA rating is based on its losses which are determined by voltage and current rather than power factor.
18). What is a No-Load Test in a Transformer?
A no-load test measures core (iron) losses by energizing the primary winding but leaving the secondary winding open.
19). What is Generator Synchronization?
Generator synchronization is the process of synchronizing the voltage, frequency, phase angle & phase sequence of 2 generators prior to joining them in parallel.
20). What is the purpose of a Phase Sequence Meter?
A phase sequence meter identifies the rotation order (R-Y-B) of a three-phase power supply to ensure proper motor direction.
21). What is an MOV (Metal Oxide Varistor)?
An MOV is a surge protector that absorbs strong transient voltages which is used to protect sensitive electronics.
22). What is the difference between Grounding and Bonding?
| Grounding | Bonding |
| Grounding connects electrical systems to the earth. | Bonding connects various metallic components to ensure equal electrical potential. |
23). What is CT Saturation?
CT saturation happens when a CT’s magnetic core becomes totally magnetized resulting in distorted output signals and a possible relay fault.
24). What are the major types of Motor Losses?
Motor losses include
- Copper losses,
- Iron losses,
- Mechanical losses, and
- Stray load losses.
25). What is Overload Protection in a Motor?
Overload protection is used to protect against the damage by disconnecting the motor when the current exceeds the specified safe limit for an extended time duration.