01
FEB, 2012
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
1
Equipment Protection
01
FEB, 2012
Equipment Protection:
Alternator Protection
Motor Protection
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
2
Equipment Protection
01
FEB, 2012
Alternator Protection
It is the heart of electrical power system as it
converts mechanical energy into its electrical
equivalent.
Also known as Generator
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
3
Equipment Protection
01
FEB, 2012
Stator Protections against Electrical Faults
Earthing and Earth Faults
• The neutral of the generator stator winding is normally earthed for protection.
• Impedance is generally used to limit earth fault current. This is when Generator is connected
direct to the distribution network.
• A setting of 10% of the maximum earth fault current is the safest for the connecting instantaneous relay.
• Time delay setting of 5% of the maximum earth fault current is applied for the connecting relay.
• Earth fault protection can be applied by using a transformer and relay to measure the secondary current.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
4
Equipment Protection
01
FEB, 2012
• Earth fault protection using a relay in parallel with a loading resistor to measure
secondary voltage.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
5
Equipment Protection
01
FEB, 2012
Overload Protection
• The amount of power that can be delivered by the prime mover may cause overloading
of the generator. This is then continuously monitored by its Governor and Regulator.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
6
Equipment Protection
01
FEB, 2012
• A Thermistor or Thermocouple embedded in the stator winding checks the rotor
winding by measuring the resistance of the field winding.
Overcurrent Protection
• An Electromechanical IDMTL relay is used to operate only under fault condition.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
7
Equipment Protection
01
FEB, 2012
Overvoltage Protection
• Overvoltage occurs at either as a high-speed transient or as a sustained condition at
system frequency.
• Overvoltage is a result of the following
Defective voltage regulator
Manual control error resulted to sudden variation of load
Sudden loss of load due to nearby circuit tripping
• Surge arresters at strategic points on the system or at generator terminals protects the
network against overvoltage.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
8
Equipment Protection
01
FEB, 2012
Rotor Protections against Electrical Faults
Potentiometer Method
• The field winding is connected with a resistance having center tap.
• The tap point is connected to the earth through a sensitive relay R.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
9
Equipment Protection
01
FEB, 2012
AC Injection Method
• An auxiliary supply is injected to the field circuit via a coupling capacitance.
• The capacitor prevents entry of high current passing through the transformer.
DC Injection Method
• A rectified voltage is injected to the
field circuit, hence eliminating the
flow of capacitance currents.
• The auxiliary voltage is used to bias
the field voltage to be negative with
respect to the earth.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
10
Equipment Protection
01
FEB, 2012
Alternator Protections against Mechanical Faults
Reverse Power
• More applied when generators run in parallel to protect the system against
the failure of prime mover.
Loss of Excitation
• A mho-type impedance relay is used to detect the condition of excitation
loss on the primary side.
Loss of Synchronization
• When the generator is synchronized, the frequency of the system will
change depending on load and the average characteristics of all the
generating units connected to the grid. Large changes in system frequency
can cause the generator to fall out of synchronism with the system.
• Protective devices on the generator will operate to disconnect it
automatically.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
11
Equipment Protection
01
FEB, 2012
Thank You for
Listening
Let’s discuss Motor Protection…
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
12
Equipment Protection
01
FEB, 2012
Equipment Protection:
Alternator Protection
Motor Protection
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
13
Equipment Protection
01
FEB, 2012
Why do we protect motors?
Every electric motor has operating limits. Overshooting these limits
will eventually destroy it and the systems it drives, the immediate
effect being operating shutdown and losses.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
14
Equipment Protection
01
FEB, 2012
Where do we protect motors?
Electrical
• power surges, voltage drops, unbalance and phase losses causing variations in the
absorbed current,
• short circuits where the current can reach levels that can destroy the receiver.
Mechanical
• rotor stalling, momentary or prolonged overloads increasing the current absorbed by the motor
and dangerously heating its windings.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
15
Equipment Protection
01
FEB, 2012
Faults in the Motor
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
16
Equipment Protection
01
FEB, 2012
Stator or rotor winding failure
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
17
Equipment Protection
01
FEB, 2012
Short Circuit Current Calaculation
3Ø X
Fault
Rated KVA x 100 100%
I SC =
√3 (ELRated) %Z
From Sample Computational Experiment No. 3
(b) Two (2) basic characteristics of prime movers for alternators operating in parallel to ensure their
successful and stable operation:
1. Their prime movers must have drooping speed characteristics and the same speed regulation.
2. Their prime movers must have speed governor mechanism so that division of load between
alternators operating in parallel can be adjusted.
(c) If the speed of alternator 2 is reduced, then its KW load will be transferred to alternator 1.
(d) If the excitation of alternator 2 is reduced, then its KVAR load will be transferred to alternator 1.
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
18
Equipment Protection
01
FEB, 2012
Thank You for
Listening
Let’s have some sample problems before having our
Preliminary Course Assessment…
TOPIC TITLE SY / TERM OF EFFECTIVITY PREPARED BY
2T / 2020-2021 L. Valcos
19
Equipment Protection
