Can Earth wire be avoided on O/H Lines?

As we I know that the earth wire is not only for lightening protection, but it serve the fastest return path for ground/earth fault protection. Though each Tower structure is grounded, but the earth resistivity between the fault point and source point is very high. In fault condition Earth wire is low resistance path back to source, thus fault protection mechanism operate w. o. any delay. 
               

         
In addition to that the continuous run of Earth wire on top of Tower structure discharge the electrostatic charge continuously around the TM line. This reduces the chances of lightening on conductor as well as structure. In addition lightening arrestors at terminal pole protect the substation equipment if for some reason lightening strike line conductors.

With today's technology the earth wire is replace with OPGW. Fiber optic + Ground wire.
The earth wire you see now has fiber optic cable, which carries all communication and SCADA signals. This segment of the Transmission line is most important and intelligent.

All these factors make the Earth wire essential hardware of Transmission line

Electrical Testing and Commissioning Of Switch Board

Electrical Testing and Commissioning Of Switch Board

Testing and start-up / commissioning procedures for all the components of medium voltage switchgear like circuit breaker, busbar, instrument transformers (current/voltage), disconnect   and grounding switches etc regardless of its size, type or industry.

Objective   

To verify the physical condition and proper connections of bus bar.

Frequency

Before commissioning of the equipment

Periodic maintenance test once in a year/planned schedule

After general overhaul

Test Equipment Required:

• Insulation test (Megger)
• Micro ohmmeter
• High voltage tester
• Torque wrench

 Test Procedure:

 Mechanical Checks and Visual Inspection:

• Inspect switchgear and all components for any physical damage / defects.
• Check nameplate information for correctness.
• Inspect enclosures for proper alignment, foundation fixing, and grounding and vermin entry.
• Inspect all covers, panels’ section and doors for paintwork and proper fit.
• Check all the transport locks are removed.
• Check for smooth and proper movement of racking mechanisms, shutter, rollers, rails and guides.
• Check proper alignment of the primary and secondary contacts.
• Check operation of all mechanical interlocks.
• Check tightness of all bolted connections.
• Check for correct phasing connection of bus bar.
• Perform mechanical check and visual inspection for breaker / Contactor as per section.
• Perform mechanical check and visual inspection for instrument transformers as per section
• Perform mechanical check and visual inspection on all disconnect / grounding switches as per section.

 Insulation Resistance Test:

It includes panel enclosure, bus bar, CT and circuit breaker. The following precautions should be taken care, before starting the testing.

A visual inspection will be made to ensure the surface dust and moisture has been removed from the component under test. Ensure the component is isolated from other connected system, which may feed back to other components or circuits not under test.

On testing, voltage shall be applied between one phase and other phases connected with ground, testing shall be repeated for other phases as mentioned above. Test voltage limits mentioned in table below:

Rated voltage	Test voltage
100-700V AC/DC	500V DC
>700 to <33000V AC	Min 2500V DC
> 33000V AC	Min 5000V DC

Ref: IS7118-3

 Contact Resistance Test:

This test is to confirm the busbar joints are connected properly and verify the tightness.

The test connection diagram is as shown in Figure below.

The test shall be done with CBs inserted and closed. Measure the contact dc resistance between panels by injecting 100A DC. This will include busbar joint, CB contact resistance, CB cluster resistance, and CT primary resistance (if applicable).

Limits:

The obtained results should be similar for all phases for each set of measurement. Other influencing factors to be considered, like length of the measured path, rating of the busbar, rating of CB, rating of CT and temperature.



Contact resistance test



  

 High Voltage Test

To determine the equipment is in proper condition to put in service, after installation for which it was designed and to give some basis for predicting whether or not that a healthy condition will remain or if deterioration is underway which can result in abnormally short life.

Test Instruments Required:

• Calibrated AC Hi-pot test set for switchgear with leakage current indicator and overload protection.
• Calibrated DC Hi-pot test set for cables with leakage current indicator and overload protection.

Check List for Switch Board Maintenance

Date:                             

Substation No:                                 

SWB No:                                                         Rating:                     

Slno	Activities	Checks carried	Remarks
1	Obtain LC from Sub-station Operation
2	Ensure isolation of the Incomer and Bus coupler breaker and control supply and Heater supply of the section
3	Ensure all back feeding sources are isolated
4	Remove all breakers/modules and PT Cubicles (If it is draw able type)
5	Open the top and side covers of the busbar chamber.
6	Clean the busbar chamber, breaker rear and front compartment with air blower, vacuum cleaner and dry cloth.
7	Clean all insulators by soft dry cloth & contact Cleaner. Check for cracks, damages & replace the defective one.
8	Check and tighten the exposed joints of the busbar. Check for any signs of heating.
9	Check and tighten the power connections of CT/ PT  and out going cables.
10	Check for any unplugged opening, missing bolts
11	Box up busbar chamber & rear compartments of breaker.
12	Check earthing system is proper & intact
13	Check IR value a) R-E       b) Y-E    c)  B-E
14	Any other abnormality

Signature

Overview of Power Distribution

OVERVIEW OF POWER SYSTEM DISTRIBUTION

power distribution



For requirement and reliability purpose the various components of a power system can be arranged in different ways. The complexity of the resulting architecture determines the availability of electrical energy and the cost of the investment.

Power distribution for a given application is therefore based on a trade-off between technical necessities and cost.

Architectures include the following:

1. Radial systems
• Single-feeder
• Double-feeder
• Parallel-feeder
• Dual supply with double bus bar
  . 
2. Loop systems
• Open loop
• Closed loop
  . 
3. Systems with internal power generation
• Normal source generation
• Replacement source generation

The table below lists the main characteristics of each architecture for omparison. Illustrations are provided below table.

Architecture	Use	Advantages	Drawbacks
Radial
Single-feeder radial	Processes not requiring continuous supply E.g. a cement works	Most simple architecture Easy to protect Minimum cost	Low availability Downtime due to faults may be long A single fault interrupts supply to the entire feeder
Double-feeder radial	Continuous processes: steel, petrochemicals	Good continuity of supply Maintenance possible on busbars of main switchboard	Expensive solution Partial operation of busbars during maintenance
Parallel-feeder	Large power systems Future expansion is limited	Good continuity of supply Simple protection	Requires automatic control functions
Double busbars	Processes requiring high continuity of service Processes with major load changes	Good continuity of supply Flexible operation: no-break transfers Flexible maintenance	Expensive solution Requires automatic control functions
Loop systems
Open loop	Very large power systems Major future expansion Loads concentrated in different zones of a site	Less expensive than closed loop Simple protection	Faulty segment can be isolated during loop reconfiguration Requires automatic control functions
Closed loop	Power system offering high continuity of service Very large power systems Loads concentrated in different zones of a site	Good continuity of supply Does not require automatic control functions	Expensive solution Complex protection system
Internal power generation
Normal source generation	Industrial process sites producing their own energy E.g. paper plants, steel	Good continuity of supply Cost of energy (energy recovered from process)	Expensive solution
Replacement source (source changeover)	Industrial and commercial sites E.g. hospitals	Good continuity of supply for priority outgoing feeders	Requires automatic control functions

Examples of Power System Architectures

Substation healthiness check

SUBSTATION HEALTHINESS CHECK



substation healthiness



a)      Substation  overall

1	Are all doors and windows locked?
2	Are all doors/shutters opening and closing smoothly?
3	Are all windows opening and closing smoothly?
4	L-drops/Tower bolts available on each door, both from inside as well as outside
5	Are window panes of all windows are in order?
6	Are there any gaps beneath the fully closed door/shutter?
7	Is DC Emergency Lights working?
8	Is Pressurization system working & what is the date of last filter cleaning?
9	Check the pressure differential and see if it is within normal limits. Record it.
10	Is Do's and Don'ts board available?
11	Is Updated SLD board available?
12	Is List of authorised persons/entrants available?
13	Is Shock treatment chart available?
14	Are Cable trench openings fully covered?
15	Are Filled sand buckets/tested fire extinguishers in appropriate numbers available?
16	Is the cable cellar free from garbage and unwanted materials?
17	Is the cable cellar well lit and free from obstructions?
18	While examining from the cellar are all the ingoing cables entries/ holes well sealed?
19	Is the substation being regularly dusted/ mopped?
20	Are the Insulating mats provided in front of all the switchgear panels?
21	Check whether thermometer and Humidity measuring device is in order. Record the readings.

b)     Transformer yard

1	Is it Easily Accessible?
2	Is there any growth of Wild grass/vegetation?
3	How is the Cleanliness (inside/outside)?
4	Is the yard properly fenced and danger board provided at a visible place?
5	Are Gates kept locked?
6	Are the terminal boxes completely sealed?
7	Is there any Gap/hole in cable entry bottom plate?
8	Is the physical appearance of Silica gel OK?
9	Is Transformer oil level ok?
10	Is there any oil leakage on the transformer tank surface?
11	Are filled sand buckets/ tested fire extinguishers available in the yard?
12	Are the neutral grounding electrode pits in good condition?
13	Are there any traces of oil leakage into the electrode pits?
14	Is the transformer surface paint in good condition?
15	Check for any abnormal humming noise emanating from the transformer.

c)      Battery room

1	Check if Light fittings & exhaust fan are flameproof construction and in working condition.
2	Check for any abnormal temperature of cells.
3	Check for electrolyte leakage from cells, if any.
4	Check for availability of tools and tackles like hand gloves, apron, electrolyte drums, funnel etc. in Battery room.
5	Check for continuous availability of water in the Battery room.
6	Is Shock treatment chart available?

d)     Sealing of hole in HT/ LT Switchgear /DCDB/ Chargers/ VFD panels etc.

1	Are Holes/cut-outs in front/back side of the panel properly covered/closed?
2	Are Front/back covers of all the feeders/breakers closed properly?
3	Are Relay modules/control cabinets of all the feeders/breakers closed properly?
4	Are any gaps through front/back covers/relay modules/control cabinets of all the feeders/breakers sealed properly?
5	Are all panel screws found in place and tightened properly?
6	Are all extra holes/cut-outs or part of these holes/cut-outs on panel completely sealed?
7	Are any gaps at the panel door hinges/side covers/ top covers properly sealed?
8	Are panel door gaskets in good condition?
8	Is there any dust/spider web on any part of the panel?
9	Are all the extra holes in the bottom cable entry plate and gaps through existing cables completely sealed (Applicable for panels under shutdown)?
10	Check whether Indication lamps are in working condition.
11	Check if any relay abnormal operation has occurred. Investigate and then reset.

e)      FLP Equipments

1	Check flame proofness of FLP equipments e.g., Lighting Luminaries, JBs, DBs, PBSs etc.
2	Check that the glanding is proper and with FLP Double Compression cable gland.
3	Check the Terminal Blocks of FLP equipments for tightness & cleanliness.
4	Check availability of all the Allen Bolts on FLP fittings/JBs/ DBs etc. Provide,  if not existing.