Transformer Loss Compensation

1
Transformer Loss Compensation

• Presented by
• Mike Coit

2
Why Use TLC?

• Billing point is different than metering point.
• Impractical to meter at billing point.
• Too expensive (High Voltage vs. Low Voltage).
• Inaccessible.
• Low voltage service changed to high voltage
  service, existing metering to be used.

3
TLC Objectives

• Determine unmetered losses between billing point
  and metering point.
• Add (subtract) the unmetered losses to (from) the
  metered quantities.
• Energy (kWh) and Quadergy (kvarh) may both be
  compensated for at the metering point.

4
Loss Compensation Methods

• Transformer Loss Meter
• A separate meter with special V2 and I2 stators
• Transformer Loss Compensator
• Losses added into standard watthour meter
  registration using a specialized compensator.
• Resistor Method
• A variation of above, using resistors for no-load
  compensation and calibration adjustments for load
  loss compensation.
• Solid State Meter with TLC capabilities

5
Transformer Losses

• Hysteresis (no-load loss)
• Energy expended from changing intensity and
  direction of magnetic flux in transformer.
• Eddy Currents (no-load loss)
• Energy expended by circulating currents induced
  within the core material
• Load Currents (load loss)
• Energy expended by load current in transformer
  windings having some resistance (I2R losses).
• Treat Line Loss compensation (if needed) as if
  its part of transformer load losses.

6
Transformer Loss Modeling

• No-load loss watts proportional to V2
• Load loss watts proportional to I2
• No-load loss vars proportional to V4
• Load loss vars proportional to I2
• Manufactures supply watts loss test results
• Loss vars are derived from the mfg. data.

7
Data required for kV2 TLC

• Rated kVA
• L-N Voltage
• Line Current
• VTR
• CTR

• No load loss watts (Iron Losses)
• Load loss watts (Copper Losses)
• Excitation Current
• Impedance
• Line Losses (optional)

Per element values
8
TLC Values calculated for kV2

• Secondary Conductance, G
• G Elem (LFE Elem watts VTR / CTR) / (Volts
  L-N)2
• Secondary Resistance, R
• R Elem ((LCU Elem watts LL Elem watts) CTR /
  VTR) / (Amps Line)2
• Secondary Susceptance, B
• B Elem (LFE Elem vars (VTR)3 / CTR) / (Volts
  L-N)4
• Secondary Reactance, X
• X Elem (LCU Elem vars CTR / VTR) / (Amps
  Line)2

9
How TLC is performed in the kV2

• Every momentary interval
• Per element losses are calculated
• Example LFE Elem wh G Elem VL-N2h
• Losses are added to or subtracted from load
  measurements
• Adjusted values are then processed normally
  (energy and quadergy is accumulated, demands are
  calculated, etc.)

10
Testing a TLC enabled kV2

• Calibration LED is unaffected by TLC
• TLC may be disabled to facilitate testing using
  displayed values or PI outputs
• Check no load losses by applying expected voltage
  only (no current) to the meter
• Note that expected voltage may differ from
  typical test voltages
• Load losses can be compared after subtracting out
  the measured load and no-load losses from the
  metered value.