Common questions

What is the use of off-load tap changer?

What is the use of off-load tap changer?

Off-load tap changers for transformers (DETC) are used to change the transmission ratio in order to adjust the transformer to grid conditions. Therefore tap changer for transformers have several pins to connect with the coil windings.

What is difference between on-load tap changer and off-load tap changer?

Unlike in on-load tap changing where the arc quenching is limited by oil when the transformer is on-load, the tapping with an off-load tap changer is only carried out when the transformer is in OFF-Switch condition.

What is off circuit tap changer?

No-load tap changer (NLTC), also known as Off-circuit tap changer (OCTC) or De-energized tap changer (DETC), is a tap changer utilized in situations in which a transformer’s turn ratio does not require frequent changing and it is permissible to de-energize the transformer system.

What are the disadvantages of tap changing transformer?

However, its major disadvantage is that although two thyristor are ON over short periods during the tap-changing process, it is permanently connected to the circuit of the deviation switches and it probably gets burnt. This may therefore reduce the reliability of the system.

Why the load is disconnected before the off load tap changing operation?

Since the taps are provided at various points in the winding single tap must be connected at a time otherwise it will lead to short circuit. Hence the selector switch is operated after disconnecting the load.To prevent unauthorized operation of an off load tap changer, mechanical lock is provided.

What voltage of on load tap changer is required for unit transformer?

Explanation: The HV voltage is relatively low, being equal to the generator output voltage, i.e. usually between 11 and 23.5 kV. The LV voltage is usually 11 kV nominal, although on some combined cycle gas turbine stations 6.6 kV is used to supply the unit auxiliaries.

What is the basic difference between distribution transformer and auto transformer?

Comparison Chart

Basis For Differences Autortransformer Conventional transformer
Connection Depends upon the tapping Connect directly to the load.
Starting current Decreases Decreases by 1/3 times.
Excitation current Small Large
Economical More Less

What is on load tap changing transformer?

Definition: An On-Load Tap Changing Transformer (OLTC) consists of an open load tap changer, it is also known as an on-circuit tap changer (OCTC). They are used in areas where there is an interruption in the power supply due to an unacceptable tap change.

Where is the tap changer is connected?

Although some tap-changers are connected on the HV winding, most tend to be connected on the LV winding. Most of these are connected at the LV winding line-end and only a few are connected at the winding neutral-end.

What is the off load tap changing transformer?

In this method, the transformer is disconnected from the main supply when the tap setting is to be changed. The tap setting is usually done manually. The off load tap changing transformer is shown in the figure below In order that the supply may not be interrupted, on-load tap changing transformer are sued.

What is a tap changer and how does it work?

Tap changers are installed in situations where they can compensate for variations in voltage. A rising or falling voltage at the load end of the line can be corrected by the action of a tap changer at the supply end. There are two possible ways of doing this—off load and on load.

What happens when a load tap changer fails?

Load tap changers (LTCs) play an important role in a substation. These mechanical devices are often overlooked, but a failed LTC will cause problems at its substation and complications through the grid as load is rerouted. LTCs are often tested and maintained by the same crews that test circuit breakers.

How on-load tap-changer is controlled by CBM?

On-load tap-changer is controlled by CBM IED (110 kV) or on-load tap-changer control IED (220 kV), The on-load tap-changer control is implemented via the logical node ATCC. DJ Allan FREng, CEng, FIEE, FIMechE, FIEEE, in Electrical Engineer’s Reference Book (Sixteenth Edition), 2003