1). What is the Primary work responsibilities of an Electrical Field Engineer?
An electrical field engineer should make supervision on installation, testing, maintenance and repair of electrical systems in the field.
Their responsibilities include:
> Supervision of site activities & ensure safety compliance.
> Inspect & test electrical systems, panels & equipment.
> Identifying issues (faults) & coordinating fixes.
> Recording field observations & generating reports.
2). What is the difference between MCB and MCCB?
Both MCB (Miniature Circuit Breaker) & MCCB (Molded Case Circuit Breaker) are protective devices, however they have different applications.
| MCB | MCCB |
| MCBs are utilized for circuits with low current often less than 100A. | MCCBs can withstand larger current ratings (up to 2500 A) & have changeable trip settings to prevent overloads. |
3). Which types of Earthing systems are used in substations?
Substations commonly use the following earthing methods:
> Plate earthing includes burying a metal plate in the ground.
> Pipe earthing consists of placing a GI pipe vertically.
> Rod earthing involves driving copper (or) GI rods into the ground.
> Grid earthing is a mesh of conductors installed underneath the substation yard.
These ensure the safe discharge of the fault currents while also maintaining equipment safety.
4). How does Insulation Resistance testing for Cables work?
To do an insulation resistance (IR) test, detach both ends (2 ends) of the cable & utilize a megger (primarily 500 V or 1 kV).
The test consists of measuring the resistance between
- Phase-to-Ground
- Phase-to-Phase
The IR value must be measured in megaohms (MΩ) and meet safety regulations based on voltage & cable length.
5). What are the most common causes of Transformer Failures On-Site?
Field transformers may fail owing to a variety of reasons:
> Overloading beyond limit.
> Moisture or water infiltration into the oil or windings.
> Insulation breakdown caused by heat or aging.
> Lightning strike (or) high voltage surges.
> Lack of regular maintenance (or) oil testing.
6). What is the role of CTs & VTs in the field?
Current Transformers (CTs) & Voltage Transformers (VTs) are utilized for measuring and protecting.
> CT converts high current into measurable numbers for meters & relays.
> VT reduces high voltage to a safe level for safety and metering.
7). How does one test a Circuit Breaker during Preventive Maintenance?
Circuit breaker testing includes several important checks:
> Visually inspect for wear, rust (or) symptoms of overheating.
> Contact resistance measurement is used to detect contact wear.
> Insulation resistance test between poles and earth.
> Functional trip testing with simulated fault current.
8). What is the difference between RCCB & ELCB?
| ELCB | RCCB |
| ELCB is an older equipment that detects earth fault voltage. | RCCB (Residual Current Circuit Breaker) trips when it detects a difference between incoming and exiting current, making it more sensitive and dependable. |
9). What safety precautions should be taken before doing Switchgear Maintenance?
Before working with switchgear:
- Isolate the power supply and confirm that LOTO (Lockout-Tagout) is activated.
- Utilize a voltage detector to establish the absence of voltage.
- Discharge any stored energy (capacitors, etc.).
- Use the proper PPE (gloves, arc suit, and safety shoes).
- Display warning signs in the work area.
10). How is Cable Megger Testing carried out on-site?
Cable Meggering involves:
> Disconnecting cable ends from the load.
> Choosing an adequate test voltage (e.g., 1kV for 11kV cable)
> Testing phase to phase and phase to earth.
> Acceptable IR values often exceed 100 MΩ.
11). What safeguards are employed for electric motors?
Motor protection comprises:
> Thermal Overload Relays for Overcurrent
> Short-circuit protection with MCCB or fuse.
> Phase failure & reversal protection
> Earth fault protection with ELCBs (or) earth fault relays
12). How do you calculate the Cable Size for a Motor?
The cable size depends on:
> Motor Full Load Current (FLC)
> Voltage Drop Limits
> Distance from the source.
> Cable’s derating factors
Use this formula:
I= P/3Vcosϕ
13). What is Loop Checking during field commissioning?
Loop checking guarantees that all control & instrument signal loops are wired appropriately and work properly.
It includes:
Check for continuity from the field to the control room.
Simulating input signals (such as 4-20 mA).
Checking the right response on SCADA, PLC, and HMI.
14). Why is earthing necessary in electrical systems?
Earthing creates a pathway for fault current and:
- Prevents electrical shocks.
- Ensures voltage stability.
- Protects the equipment from damage.
- Helps in the operation of protection devices.
15). What is a Busbar? What are different types?
A busbar is a conductor used to distribute power within panels (or) substations. Types include:
- Single busbar.
- Double busbar
- Ring busbar.
- Main & transfer bus configurations
16). What are the commissioning tests for Transformers?
Transformer commissioning involves:
> Infrared and PI Test
> Turns ratio Test (TTR)
> Winding Resistance Test
> Magnetizing Current Test
> Vector group verification Test
> Oil BDV & moisture analysis.
17). What is the purpose of OLTC in transformers?
The On Load Tap Changer (OLTC) regulates voltage without interrupting the power supply by modifying the turns ratio under load conditions.
18). How do you troubleshoot a tripped breaker on-site?
Steps include:
Step-1: Determine whether it is overload or short-circuit related.
Step-2: Inspect the linked load for problems.
Step-3: Check the breaker settings and age.
Step-4: Reset only after ensuring that the fault is cleared.
19). Which types of Switchgear are utilized in Substations?
Depending upon the voltage level:
LV switchgear: ≤ 1kV
MV switchgear: 1kV–33kV
HV switchgear: > 33 kV
Types of switchgear include air-insulated, gas-insulated, metal-clad & vacuum.
20). How is a diesel generator (DG) checked prior to commissioning?
Testing includes:
> Checking fluid levels (fuel, oil, and coolant).
> Battery Voltage & Cranking
> No load running
> Load test (at 25%, 50%, 75% & 100%)
> Verifying protective features and alerts.
21). How are Cable Failures detected in the field?
The techniques employed are:
> Time Domain Reflectometers (TDR),
> Pulse echo method,
> Insulation Resistance Test,
> Using surge generators to pinpoint faults.
22). What is the purpose of Lightning Arrestors?
Lightning arresters are ustilized to protect the equipment against voltage spikes induced by lightning (or) switching. They safely divert surge voltage to the ground.
23). What is an appropriate IR value for an 11kV motor?
Generally, the IR value must exceed:
100 MΩ for the new motors.
Motors in operation must have a minimum resistance of 10 MΩ, depending on age & condition.
24). Which documentation should be reviewed prior to field execution?
Always verify:
> Single line diagrams (SLDs),
> Cable scheduling and route drawings,
> Load list & control schematics,
> Manufacturer’s installation manuals,
> Method for statement and risk assessment.
25). How do you read & interpret a Single Line Diagram (SLD)?
SLD allows you to understand the entire power flow, from the entering supply to the end loads. You must identify:
- Main breakers, CTs, and VTs,
- Loads & their feeders,
- Protection relays & metering.