There are three major
components to a tap changer. These are:
- • Motor Drive Mechanism
- • Tap Changer Assembly
- • Tap Connections to the Bank Winding
The Energy Control Center is specifically responsible for coordinating
voltage control throughout the DWP Power System
If the output voltage is too low, the generator may
- fall out of synchronism
- with the Power System.
The two major types of banks used for voltage control at receiving
- • Main power banks
- • Line banks
Unlike synchronous condensers, static capacitors provide a
Synchronous condensers can either supply or consume VAR
- VAR closer to
- the load than the generators. This relieves generators of VAR and
- reduces line losses.
Synchronous condensers make variable adjustments for
Synchronous condensers are normally connected to
13.8kV tertiary winding of main power banks.
Main power banks at receiving stations reduce voltage to the
subtransmission voltage level.
tertiary winding on a bank connects
the condenser to the bank
Some line banks have LTCs that can affect
the transmission voltage
station banks with either LTCs or LRCs can directly and automatically
adjust the distribution voltage
Most step regulators have a neutral plus
- 16 5/8% steps up and 16 5/8%
- steps down. This provides a total of 33 different settings.
Pole-top static capacitors provide
VAR close to the load for the greatest efficiency
Any malfunction in voltage control equipment that prevents the
equipment from maintaining voltage schedules is
Class A trouble
+ VARs vs - VARS
- +VARS going down stream to: going out
- -VARS go up steam :coming in
Putting more bank
on raises voltage off lowers voltage
Increasing the field voltage raises voltage and increases
Decreasing the field voltage lowers voltage and
While 34.5kV capacitors are usually
bus connected, 4.8kV capacitors may be connected
- to either a bus or a
Increasing Voltage increases
You should check voltage regulators for automatic operation. Do this
- • Taking the regulator on manual control
- • Run three (3) steps in either direction
- • Check that the regulator returns to approximately the same step
If you are unable to repair the regulator, block it on
- a compatible step
- and report
Law of Electrical Charges is a
fundamental law of electricity. It states, in part,
, that unlike-charges attract and like-charges repel.
The pressure or force that causes free electrons to move in a conductor
is referred to as either
- • Electromotive Force
- • Difference in Potential
- • Voltage
The speed of current is
constant 186000 mph
One ohm is defined as
- as the resistance of a circuit that permits a steady current of
- one ampere to flow when one volt is applied to a circuit
The lower case letter m stands for milli or the fraction
Ohm's law can be expressed in the equation
E = I × R
Calculating resistance in series
add them together
Calculating resistance in paralell
1/Rt = 1/R1+ 1/R2 + 1/R3 ect.
- Req = R1*R2
- R1 + R2
The opposition to current flow that is produced merely by aconductor's inability to perfectly conduct current is resistance.
- Electrostatic fields surround all conductors that are energized.
- The transfer of energy through this electrostatic field is known as CAPACITANCE. Capacitance reacts to changes in the circuit voltage.
- The greater the "rate of change" in voltage, the greater the capacitance
- on the circuit
The formula for power factor in an AC circuit is:
pf= R ÷ Z
Power factor formula
Pf= TP / AP
Apparent power is
VARs ie. VA
If you know the value of the LINE amps, you can find the value of the
phase amps by the following formula
Aφ = AL/1.73
how to calculate the amperage of a WYE line
The phase equals the line
how to calculate the voltage of a line from the phase
V of phase = VLine / 1.73
how to find voltage of a line in a DELTA system
Vphase = Vline
Diff between formula for WYE and DELTA
- DELTA : voltage the same line
- Amp = amps / 1.73
WYE : amps the same as line
A transformer is basically two sets of coils on a magnetic core of some
kind. It has no moving parts and works on the principle of
When a load is applied to the secondary windings, load current will
appear in both windings. These currents are
inversely related to the turns-ratio of the windings.
The flow of current in the primary circuit is governed by three factors:
- • Characteristics of the source, voltage and frequency
- • Impedance of the winding
- • Strength and direction of the magnetic field in the iron core.
The voltage induced in the secondary coil is also governed by three
• Strength and direction of the magnetic field in the iron core.
- • Rate of change in the magnetic field
- • Number of turns in the coil.
Eddy currents are circulating currents that are
induced in the core of a transformer. They are the result of the alternating magnetic flux produced by the transformer windings.
Hysteresis losses are the result of the molecules of the core material
magnetized and de-magnetized.
Copper losses are an additional transformer loss. They are due to the
a transformer winding to the magnetizing current
Oil in a transformer has two purposes:
- • Insulating the transformer, and
- • Cooling the transformer
Oil functions to cool the windings and core of the transformer by a
The limiting temperature is ________ (winding) for modern transformers.
The maximum top oil
temperature is ______ for normal operation
There are three general methods for
increasing cooling rate seen in DWP transformers:
- 1. Increase Surface Area of Tank.
- 2. Increase the Rate of Air Movement.
- 3. Increase the Rate of Oil Circulation
FA FOA OA
FA = Forced air
FOA = Forced Oil Air
OA = Oil Air aka convection cooled
This type of bushing has a central conducting rod through which the
conductor passes. Surrounding the rod is a series of insulating barriers
held apart by spacers and enclosed in an oil filled porcelain skirt.
This bushing is similar to the Oil-filled except that the central rod is
wound with alternating layers of insulation and tin foil.
A typical instrument transformer ratio is ______
400 to 1