Transformer Nameplate: Meaning of Data

Transformer Nameplate:

Voltage Rating (V), Kilovoltampere Rating (KVA), Frequency (f), Number of Phases, Temperature rise, cooling class, percent impedance, name of manufacturer etc. data are given by a Transformer nameplate. In the large power transformers nameplate also include Basic Impulse Level, Phasor Diagrams for 3-phase operation and tap changing information.

Voltage Rating

No-load values are voltage rating, high side and low side etc. Full-load values depend on the connected load’s power factor, so this data are not given on nameplates only No-load data are given. Voltage rating in No-load include a winding designator such as a Long dash (─), Slant (/), Cross (×), or Wye (Y) to indicate

Dash (─): Indicates voltages are from different windings.

Slant (/): Indicates voltages are from same winding.

Cross (×): Indicates voltages that may be obtained by reconnecting a two part winding in series or parallel. This type of winding is suitable for single wire operation.

Wye (Y): Indicates voltages in a wye connected winding.

Examples for Voltage Rating:

Single Phase:

240 / 120: 240V winding with a centre tap.

240 × 120: Two-part winding that may be connected in series for 240V, or connected in parallel for 120V.

240 ─ 120: A 240V winding and a separate 120V winding.

Three Phase:

 4160 ─ 440Y / 260: A 4160V delta connected winding, and a separate 440V wye connected winding an available neutral connection. The voltage of the delta winding is always given first.

Frequency: Transformers rated frequency.

KVA: Transformers rated apparent power (Kilo Volt Ampere).

Percent Impedance: At the indicated temperature, the percent impedance of the transformer measured.

Temperature Rise: Based on an ambient temperature of
30˚C, the maximum allowable temperature rise of the transformer.

Class: The insulating medium and the cooling method.

BIL: The Basic Impulse Level or BIL of a transformer is a method of expressing the transient voltage stress that the insulation of transformer will tolerate without damage.

Using Transformer Nameplate:

In present Day, you can find the following minimum information and Data on a transformer nameplate. The following information and data for above 500 kVA transformers:

• Name of manufacturer
• Serial number
• year of manufacture
• Number of phases
• kVA or MVA rating
• Frequency
• Voltage ratings.
• Tap voltages.
• Connection diagram.
• Cooling class
• Rated temperature in °C
• Polarity (for Single Phase Transformers)
• Phasor or vector diagram (For Polyphase or Three Phase Transformers)
• % impedance.
• Approximate mass or weight of the transformer
• Type of insulating liquid.
• Conductor material of each winding.
• Oil volume (of each transformer Container/Compartment)
• Instruction for Installation and Operation

Figure: A Transformer Nameplate