Medium Voltage Panels

The medium voltage panel normally consists of set of incoming breakers, outgoing breakers, bus couplers, bus risers and measuring cubicles.

The service activity for the panels and cubicles includes the following: –

• Bus bar tightening for active and passive parts
• Bus bar continuity check with Micro-ohm meter
• Bus bar insulation check up to 50 KV
• Mechanical alignment of the cubicles
• Space heaters testing and maintenance
• Shutters and doors maintenance

Medium Voltage Circuit Breaker

The medium voltage circuit breaker is the most important device in the MV system as it is responsible for clearing the fault by very fast switching and great ability to extinguish the arcs and sparks. There are different types of the breakers according to the voltage rating, current rating and the media (SF6, Oil, Air or Vacuum).
To ensure the proper operation of the breaker, there are main factors to be secured.

The service activity for the circuit breaker includes the following: –

• Circuit breaker contact resistance measurements
• Circuit breaker opening and closing timing measurements
• Testing The synchronization of the three poles of the breakers
• Maintenance of the breaker mechanism to get the proper timing
• Maintenance of the breaker contacts for the proper resistance
• Breaker carriage maintenance for proper positioning
• Maintenance of the breaker connection with the bus-bar

Protection Relays

The protection relay is an essential part in the power distribution system; this part is the system guard against abnormal operating conditions and faults. There are many types of relays’ classifications according to the function, like, over current, short circuit, over voltage, reverse power, etc. or according to the construction, like, electromechanical, solid state , digital and microprocessor based relays.

The service activity for the protection relays includes the following: –
• Function test and characteristic curve validation
• Calibration, secondary and / or primary injection
• Wiring interconnection check with the breakers and indicators
• Upgrading and modification of old electromechanical relays

Power Distribution Transformers

The power distribution transformers are the main link between the medium voltage system and the low voltage system, these transformers are subjected to different type of testing, some of the test are carried out for the new installation or after repair, like the following: –
• Turns ration and voltage ration testing at different taps
• Winding resistance measurements
• Winding insulation testing

There are some tests related to the oil type transformers, these tests are carried out either on line or off line, like the following: –
• Oil Dielectric strength testing up to 60 KV
• Oil hydrant test for H2 equivalent gases contents
• Oil acidity testing

The service activity for the transformer includes the following: –
• Oil testing and analysis
• Silica Jill condition monitoring and change, if needed
• MV and LV bushings cleaning, and tightening.
• Oil gaskets condition monitoring and change, if needed
• Insulation testing with and / or without cables

Low Voltage Panels

The low voltage panels are the last station to which the power transformer output is connected and the load are supplied from there, these panels include

• Incoming circuit breakers
• Bus bars and couplers
• Outgoing feeders
• Motor control centers (MCCs)

The service activity for the low voltage panels includes the following: –
Primary or secondary injection test

• Open and close time test
• Contact resistance test.

Power Factor Correction Panels

The power factor is one of the important measures in the power distribution network, indicating the efficiency of power and equipment utilization in the system, the low power factor results in overloading the elements of the power distribution network without getting the maximum active power out of the system.
The power factor correction panels include the following items

• Power Capacitors
• Protection Fuses
• Power Factor Regulator
• Measuring Instruments (Current and Voltage Transformers)
• Switching Devices (Contactors)
• Harmonic Filters / Reactors

The service activity for the power factor panels includes the following: –
Actual measurements for PF and Harmonics
• Testing and Adjustment of the Regulators
• Testing of capacitor elements
• Review and check the fuses and contactors