Electrical Inspection, How To perform It?

Electrical Inspection, How To perform It?
electrical inspection

Electrical inspection for electrical devices and equipment is just like medical health care inspection for your body, The common thing is that this inspection should be done periodically to keep the equipment in good condition.

In this important article we will discuss how to perform effective electrical inspection for transformers, motors, distribution panels, lighting systems and more?

Electrical inspection for transformers

Electrical transformers are some kind of machines! but static machines with no movement, and to keep this machine in good condition you should make electrical inspection periodically.
This electrical inspection guide will provide you with the most common check points for electrical transformers, but firs we need to know parts of transformer to be able to prepare a proper inspection for each part.

Electrical transformer main parts

Transformers consists of active and inactive parts, the active parts are windings and iron core, while inactive parts are any other parts.
Inactive parts aren’t negligible but are necessary for transformer safety and proper operation.

Active parts of the transformer

  • Winding (primary and secondary)
  • Iron core (in core type transformers)

These are the parts of transforming voltage and current, primary (connected to the power source), and secondary windings (connected to load) reduce or increase voltage according to the ratio between turns number of primary and secondary.

Inactive parts

All other parts except winding and core are called inactive parts, These parts are like transformer oil, silica gel breather, cooling radiator, temperature gauge, conservator tank and all other parts. For more details about transformer parts read my article, transformer, types, active and inactive parts.

Transformer electrical inspection

Inspection before energizing the transformer:

Before the transformer is energized some visual inspections should be done as follows:

  • check nameplate of the transformer, and compare the data with the project requirement (i.e. primary and secondary voltage, frequency, KVA rating etc.)
  • check oil level in the conservator tank, make sure its 1/3 volume is full.
  • check for any oil leakage on transformer body.
  • check that radiator has no plastic bags or birds nests between its sections.
  • check for any mechanical damage due to transportation.
  • check all bolts are well tightened.
  • check cooling fans number and connection
  • check protection of the transformer (like buchholz and sudden pressure relay).
  • make sure that high and low voltage insulators are in good condition and clean.

After connection and energizing the transformer

After the transformer is connected but before it is energized make sure that primary and secondary windings are connected to the right side, then energize loads.

After loading the transformer keep inspecting its temperature rise and make sure its not exceeding the designed one on the nameplate, The temperature is shown on the gauge but its better to use temperature detector to ensure that the gauge working properly.

While the transformer is in service the same electrical inspection mentioned above should be done periodically to keep the transformer condition under your eyes, and every one year the oil of the transformer should be tested and analyzed to make sure it still clean and moisture free.

Induction motor electrical inspection

Induction motors could be divided in two, Single phase and three phase induction motors, Most inspection and maintenance programs for both types are the same.

Motors parts

The main parts of induction motors are stator and rotor, In some larger size motors some instruments are added such as space heaters, thermo-couples, cooling fans and junction box.
Each of these parts and accessories need maintenance program, this what we will discuss below.

     Motor electrical inspection before installation

Before connect the induction motor and energizing it you as an electrical engineer or electrician should check name plate data as following points:

  •  voltage and frequency must be suitable to the source.
  • current should be checked and double checked to check the motor control panel devices, set over-current protection and also to check the size of the cable feeding the motor.
  • motor rotational speed (RPM) should be suitable for the mechanical load.
  • frame of the motor should be suitable for installation condition and place.
  • explosion proof protection of the motor if needed.
  • motor connection, star or delta connection.

   After connecting and energizing the motor

  • check and measure grounding of the motor body, its resistance is accepted below 5 Ω.
  • check voltage between motor phases and compare it to name plate value.
  • measure motor current in both cases, no-load and loaded compare with rated value.
  • check rotation direction.
  • listen carefully to the motor for any abnormal noise.
  • after loading the motor for at least two hours, check its temperature.

   Motor periodic inspection

The motor is in service, works well and causes no issues, that’s good, but not mean that no preventive maintenance needed for the motor.

Monthly electrical inspection

While the electrical motor is in service a good preventive maintenance should be performed carefully, keep measuring and recording voltage, current, grounding and temperature values every one month, and keep comparing with nameplate values.

Lighting electrical inspection

Lighting fixtures and lamps are used in all work locations and fields, In your house lamps are controlled by a switch, But in large industrial locations lighting fixtures are controlled by panels contains relays, MCB‘s, photocell, contactors and many components, the main job of lighting panels is to auto control lighting, this auto control switch on lights at night and turn it off at day light.

Periodic inspection for lighting fixture

Lighting fixtures electrical inspection is cost-less, All you need is to be focused each lamp, Then every day you should have a clear vision of how many lamps are not working.

Lighting control panels inspection

Like any electrical panel, keeping the panel not sealed allows dirt and dust to enter the panel and make connection issues for contactors, MCB’s and connection terminals. In some cases dust and humidity or rain cause serious short circuit inside the panel.

Check points for lighting panels

  • check panel door and openings, all should be sealed.
  • check contactors for abnormal noise.
  • clean the panel if it has any dust, But isolate power first.
  • check voltage and record its value.
  • test the operation of the photocell by covering it with a black piece of paper, lighting should work.
  • check wiring for loosen connections and corrosion terminals.
  • make sure that the panel is grounded, measure the grounding resistance and record it.