
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
stations are:
 • 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
the
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

Distributing
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.

Poletop 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
capacity on
on raises voltage off lowers voltage

Increasing the field voltage raises voltage and increases
VAR

Decreasing the field voltage lowers voltage and
decreases VAR

While 34.5kV capacitors are usually
bus connected, 4.8kV capacitors may be connected
 to either a bus or a
 bank.

Increasing Voltage increases
VARS

You should check voltage regulators for automatic operation. Do this
by:
 • Taking the regulator on manual control
 • Run three (3) steps in either direction
 • Check that the regulator returns to approximately the same step
 automatically

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 unlikecharges attract and likecharges 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
one thousandth.

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.

R.eq formula
 Req = R1*R2
 _______
 R1 + R2

Resistance AC
The opposition to current flow that is produced merely by aconductor's inability to perfectly conduct current is resistance.

Capacitive Reactance
 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
WYE System
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 turnsratio 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
factors:
• 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
being
magnetized and demagnetized.

Copper losses are an additional transformer loss. They are due to the
resistance of
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
convection process

The limiting temperature is ________ (winding) for modern transformers.
105°C

The maximum top oil
temperature is ______ for normal operation
95°C

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.
OilFilled Bushings

This bushing is similar to the Oilfilled except that the central rod is
wound with alternating layers of insulation and tin foil.
Condenser Bushing

A typical instrument transformer ratio is ______
400 to 1

