Troubleshooting # 01

Yesterday we  received a call from one of our clients, that whenever they  switch  on its VCB Trolley of 11KV Protection Panel tripping occurs in both the Metering Panel and also the Grid End Consumer Panel. 

When our team reached there site we did the following things.

• We checked the panels protection relay, all instantaneous tripping flags were down.
• We disconnected there INCOMING and OUTGOING cable.
• Removed the Trolley from the Panel.
• Checked The Trolley's Insulation of both the three Interrupters and also the resistance of three phases w.r.t ground, which was low as we expected.
• Then we checked the Insulation of all the panel circuit w.r.t ground, which was also low.

Note: Due to this low resistance Panel was not standing on 11KV.

         The resistance level for 11KV min. 22MΩ

Reasons:

When we inspected the Panel room and its  surroundings, we came across following causes of this fault

• High humidity/moisture level.
• Panel Room size less than recommended.
• No Proper Ventilation.
• 1window in the room without rain protection.
• An uncovered water trench in front of the room.

Three Phase Transformer connections

•  Wapda Transformers has a DY11 Connection.

Definition of Different Transformer Types and Parts according to IEC

Transformer Types
1. Power Transformer
A static piece of apparatus with two or more windings which, by electromagnetic induction,
transforms a system of alternating voltage and current into another system of voltage and
current usually of different values and at the same frequency for the purpose of transmitting
electrical power.
2. Auto-Transformer 
A transformer in which at least two windings have a common part.
3. Booster Transformer
A transformer of which one winding is intended to be connected in series with a circuit in order
to alter its voltage and/or shift its phase. The other winding is an energizing winding
4. Oil-Immersed Type Transformer
A transformer of which the magnetic circuit and windings are immersed in oil.
5. Dry-Type Transformer
A transformer of which the magnetic circuit and windings are not immersed in an insulating
liquid.
6. Oil Preservation System
The system in an oil-immersed transformer by which the thermal expansion of the oil is
accommodated. Contact between the oil and external air may sometimes be diminished or
prevented.

Terminals and neutral point
1. Terminal
A conducting element intended for connecting a winding to external conductors.
2. Line Terminal
A terminal intended for connection to a line conductor of a network.
3. Neutral Terminal
a) For three-phase transformers and three-phase banks of single-phase transformers:
The terminal or terminals connected to the common point (the neutral point) of a star-
connected or zigzag connected winding.
b) For single-phase transformers:
The terminal intended for connection to a neutral point of a network.
4. Neutral Point
The point of a symmetrical system of voltages which is normally at zero potential