Each substation and the individual items of equipment contained therein should be periodically inspected. The recommended frequency of these inspections is monthly.

Visual inspections should encompass the total substation area including the site, the control house and all equipment and structures. This inspection should be made with the substation energized. Therefore, all inspections should be made from ground level, to assure adequate safety clearances from energized parts. Binoculars should be used to view buses and other equipment located on structures.

Special care should be used when ground connections are checked, since a high voltage could develop across any gap created between a ground cable and a piece of equipment, particularly under fault conditions. For this reason, ground connections should not be removed for any reason while the substation is energized.

The following describes details of visual inspection:

Power Transformers

1. Inspect control cabinet, control relays, contactors, indicators, and the operating mechanism.
2. Look for loose, contaminated, or damaged bushings, loose terminals, and oil leaks.
3. Check oil levels in main tanks, tap changer compartment, and bushings.
4. Inspect inert gas system (where applicable) for leakage, proper pressure, etc.
5. Read and record operations counter indicator associated with load tap changer.
6. Observe oil temperature. The oil temperature should not exceed the sum of the maximum winding temperature as stated on the nameplate plus the ambient temperature (not to exceed 40° C) plus 10° C. Generally, oil temperature does not exceed 95° and 105° C for 55° C and 65° C winding temperature rise units, respectively, since the ambient temperature rarely exceeds 30° C for periods of time long enough to cause an oil temperature rise above these points.

Voltage Regulators

1. Perform the same inspections as listed for power transformers (as applicable).
2. Place regulator control in manual position and operate regulator over small range only.
3. Return control to automatic and verify that the regulator functions properly.
4. Read and record operations counter indicator.

Oil, Vacuum, SF₆ and Air Blast Circuit Breakers

1. Check for loose, contaminated, or damaged bushings, loose terminals, oil leaks, and proper gas pressures.
2. Check oil level in bushings and main tank (as applicable).
3. Check anti-condensation heaters.
4. Read and record the number of operations indicator. If breaker has not operated during the preceding year, bypass the breaker or otherwise remove the breaker from the circuit for testing. Test the breaker by simulating relay action by placing a jumper across the tripping contact studs on the back of the relay. Allow breaker to go through its sequence to check its operation.
5. Inspect contact areas on main plug-in assembly for signs of overheating or arcing.
6. Read and record compressor operating hours indicator.

Fuses

1. Observe condition of contact surface of fuse clips.
2. Check for broken or cracked supporting insulators and for contamination.

Surge Arresters

1. Check for cracked, contaminated or broken porcelain, loose connections to line or ground terminals and corrosion on the cap or base.
2. Check for pitted or blackened exhaust parts or other evidence of pressure relief.
3. If discharge counters are provided, check connections and record the number of operations.

Buses and Shield Wire

1. Inspect bus supports for damaged porcelain and loose bolts, clamps or connections.
2. Observe condition of flexible buses and shield wires.
3. Inspect suspension insulators for damaged porcelain (include line entrances).

Capacitors (Series and Shunt)

1. Observe condition of fuses.
2. Inspect for damaged tanks and bushings and for leakage of the dielectric.

Reactors (Oil Filled and Air Core)

1. Observe condition of paint and varnish.
2. Inspect bushings for cracks and contamination.
3. Check valves and gaskets for oil leaks (as applicable).

Disconnects and Other Switches

1. Check for cracked, contaminated, or broken porcelain, loose connections and corrosion to metal parts.
2. Observe condition of contact surfaces and area around them.
3. Observe condition of arcing horns on air break switches (where applicable).
4. Inspect operating mechanism.
5. Inspect all live parts for scarring, gouging, or sharp points that could contribute to radio noise or corona.
6. Inspect flexible braids or slip-ring contacts used for grounding for corrosion, wear or broken strands.
7. Check gearboxes for signs of moisture and corrosion.
8. Check corona balls and rings for damage.

Control and Metering Equipment

1. Check current and potential transformers for damage to cases, bushings, terminals, and fuses. Verify the integrity of the connections, both primary and secondary.
2. Observe the condition of control, transfer, and other switch contacts, indicating lamps, test blocks and other devices located in or on control cabinets, panels, switchgear, etc. Look for signs of condensation in these locations.
3. Examine meters and instruments externally to check for loose connections and damage to cases and covers. Note whether the instruments are reading or registering.
4. Open and close each potential switch on the test block to determine whether the speed of the meter disk is affected. Repeat the process with the current switches. Changes of speed should be approximately the same for each meter element.
5. Check status of relay targets (where applicable).
6. Make an external examination of relays, looking for damaged cases and covers or loose connections.
7. Check station battery for loose connections and the battery cells for low electrolyte level and low specific gravity of the electrolyte.
8. Inspect station battery charger. Check charging current and voltage. Observe ground detector lamps for an indication of an undesirable ground on the dc system.
9. Check annunciator panel lights.

Structures

1. Inspect all structures for loose or missing bolts and nuts.
2. Check for damaged paint, galvanizing, and signs of corrosion.
3. Inspect for deterioration, buckling, and cracking.

Grounding System

1. Check all above grade ground connections at equipment, structures, fences, switch operator’s platforms (mats), etc.
2. Observe the condition of any flexible type connections.

Cable

1. Inspect exposed sections of cable for physical damage.
2. Inspect the insulation or jacket for signs of deterioration.
3. Check for cable displacement or movement.
4. Check for loose connections.
5. Inspect shield grounding (where applicable), cable support, and termination.

Foundations

1. Inspect for signs of settlement, cracks, spalling, honeycombing, exposed reinforcing steel, and anchor bolt corrosion.

Substation Area (General)

1. Verify existence of appropriate safety signs (i.e., danger and warning signs, as applicable).
2. Check indoor and outdoor lighting systems for burned-out lamps or other component failures.
3. Verify that there is an adequate supply of spare parts and fuses.
4. Observe the condition of hook sticks.
5. Inspect the fire protection system and the provision for drainage in the event of leaking oil.
6. Check for bird nests or other foreign materials in the vicinity of energized equipment, buses, or fans.
7. Observe the general condition of the substation yard, noting the overall cleanliness and the existence of low spots that may have developed.
8. Observe the position of all circuit breakers in the auxiliary power system and verify the correctness of this position.
9. Inspect the area for weed growth, debris, and only minor material associated with the maintenance of the substation equipment stored in the yard.

Substation Fences

1. Check for minimal gap under the fence and gate. Normally the gap should not exceed 2 inches (5 cm) under the fence and 4 inches (10 cm) under the gate.
2. Check that the fence fabric is intact with no rust.
3. Check that the barbed wire is taut.
4. Check that the gate latches are operable.
5. Check that flexible braid type connections are intact.
6. Verify that no wire fences are tied directly to the substation fence.

If you would like more information or have any questions, please call Mike Eskandary, Electrical Engineer, Transmission Branch, at (202) 720-9098.