ISOLATOR of different types used in power system.pptx

ODISHA POWER TRANSMISSION CORPORATION LTD……
Sri K. C. Bisoi
Dy. Manager (Elect.)
PTC, Chandaka

 The open contacts of circuit breaker cannot be visible physically from
outside
 There must be some arrangement so that one can see open condition
of the section of the circuit before doing any maintenance work for
safety practices
 Isolator is a mechanical switch which isolates a part of circuit from
system as when required
 Electrical isolators separate a part of the system from rest, for safe
maintenance works
IEC 129 or IS 9921

 The minimum necessary condition for operation of Isolator is “During
operation the current flowing through it must be ZERO”.
 An isolator must not make or break load or fault current. It is also known as
“OFF LOAD Switch”
 It is a mechanical switch which separates a part of the electrical power system
normally at off load condition
 Electrical isolation of various equipment from the live parts for maintenance
work.
 It provide alternate path for power supply at time of maintenance work
 Isolating faulty equipment
 Transfer of load from one bus to another

Horizontal Break
 Center break
 Double Break
Vertical Break
Pantograph

Center Break Isolators
 The contact arm is divided into two parts one carries male contact
and other female contact.
 The contact arm moves due to rotation of the post insulator upon
which the contact arms are fitted.
 Rotation of both post insulators stacks in opposite to each other
causes to close the isolator.
 Counter rotation of both post insulators stacks open the contact arm
and isolator becomes in off condition.
 The normal operation of isolator is motorized but for emergency
hand driven mechanism is also provided.

Isolator open (On Load)
Isolator Close

Double Break Isolators
 These have three stacks of post insulators
 The central post insulator carries a tubular/ flat male contact which
can be rotated horizontally with rotation of central post insulator. This
contact is also called moving contact.
 The female type contacts are fixed
on the top of the other post
insulators which fitted at both
sides of the central post insulator.
 The female contacts are generally
in the form of spring loaded finger
contacts.

 The rotational movement of male contact
causes to come itself into female contacts
and isolators becomes closed.
 The rotation of male contact in opposite
direction make to it out from female
contacts and isolators becomes open.
 Rotation of the central post insulator is
done by a driving lever mechanism at the
base of the post insulator and it connected
to operating handle or motor of the isolator
through a mechanical tie rod.
Double Break Isolators
Double break Isolator open
Double break Isolator Close

 The operating contact and
arm moves in vertical plane
to open or close the isolator.
 The fixed contact is mounted
on one pole of the isolator
 The moving contact on other
pole, which moves with
insulator, by the operating
rod.
Isolator operation
Isolator Operation

 It require less ground area.
 The base of the isolator is the frame on
which stands the post isolator carrying
the head piece with the pantograph
and the gear box.
 The actuating force is transmitted to
the gear box by a rotating insulator.
The suspended contact is mounted on
the bus bar situated above the
disconnector.
Isolator operation

Single Isolator
Double Isolator
Beam mounted isolator
Tandem/off set isolator
Isolator with single E/S,
double E/S or without E/S.

Tandem Isolator Beam mounted Isolator
Isolator with single E/S Isolator with out E/S

 It used to provide permanent
earthing of the equipment, circuit
under maintenance.
 Generally E/S are provided with the
isolators so that the equipment or
circuit which was isolated by the
isolator for maintenance can be
earthed by earth switch provided in
the same isolators.
 An interlock is provided for locking
the main blades and earth
switches. Earth Switch Opening
Earth Switch Closing

1. Contacts
 It shall be heavy duty, self aligning & high pressure line type
contacts made of high purity, high conductivity, corrosion
resistant, hard drawn electrolytic copper of adequate thickness &
contact area.
 The contact area are silver plated >25 micron thickness
 Arching contact are made up of hard drawn electrolytic copper
(make before and break after)
 The contact springs are not for current carrying so it should not be
damaged due to over heating.

2. Blades
 All metal parts are of non rusting/corroding material
 All current carrying parts shall have high conductivity electrolytic
copper/alumunium
 Isolator & E/S shall be so constructed that it shall be locked in
closed/open position and not to be disturbed in case operating
shaft becoming disconnected.
 Isolator & E/S are designed in such a way that 1000 operations or a
life time of five years can be achieved before any maintenance.

3. Fixed Contact
The contacts which are fixed at both end in case of double isolator
4. Moving contacts
The contact which is fixed at center and moving in horizontal plane to
be closed with the fixed contact
5. Insulator stack
The post insulators are of creepage distance as follows:
 21mm/KV for normal area
 25mm/KV for polluted area
 31mm/KV for most polluted area

6. Elevator Plate
The plate on which the insulator is placed which is above the Base Chanel.
7. Base Chanel
The poles of disconnector placed on a complete galvanized base provided
with holes and designed for mounting on structure.
 These are made up of hard drawn copper
 Make before and break after: it closes before closing
of main contact and it breaks after main contact is
fully opened.
 The arching due to charging current in line, breaking
of bus transfer current.
8. Arching Contact

Types of Testing
Type Test
Routine
Test
Special Test

A) Power frequency withstands voltage test on the equipment
and its auxiliary equipment.
The isolator under test should withstand the voltage at power
frequency (50 Hz).
B) Temp. rise test
Temperature rise tests are used to make sure that the product does not
get overheated during operation.
The maximum temperature rise can be determine after continuous
full load run. The ambient temperature and time of test should be
stated in the test certificate.
400KV 220KV 132KV 33KV
Across the Isolating
distance
610KV 530KV 315KV 80KV
To earth 520KV 460KV 275KV 70KV

C) Rated short time withstand current test
The isolator under test should carry the rated short time current for
3sec.
D) Short circuit making capacity of Earth Switch
The earth switches to which a rated short circuit making current has
been assigned shall be capable of making at any applied voltage, up
to and including that corresponding to their rated voltage, any
current up to and including their short circuit making current.
400KV 220KV 132KV 33KV
Short Time Current 40/63KA 40KA 31.5KA 25KA

E) Mechanical Endurance test
The mechanical endurance test shall consist of 1000 operating
cycles without voltage on, without current in the main circuit
F) Lightening impulse voltage test
The isolator design in such a way that it can
withstand the rated lightening impulse
voltage without any abnormality.
LIWV (KVp) 400KV 220KV 132KV 33KV
Across isolating
distance
1425
(+240)
1200 750 195
To Earth 1425 1050 650 170

G) Switching impulse voltage test
The isolator design in such a way that it can withstand the rated
switching impulse voltage without any abnormality.
H) Pollution test
 This tests are intended to provide information on the behaviour of
external insulation under pollution.
 Tests are performed to prove that a test voltage equal to Vm/will be
withstood at the specified degree of pollution
SIWV (KVp) 400KV 220KV 132KV 33KV
Across isolating distance 900(+345) 530 315 80
To Earth 1050 460 275 70

I) Partial Discharge test
partial discharge (PD) is a localised dielectric breakdown of a small
portion of a solid or liquid electrical insulation under high voltage
stress.
 PD usually begins within voids or cracks, within a solid dielectric
 With the partial discharge measurement, the dielectric condition of
high voltage equipment can be evaluated, and electrical treeing in
the insulation can be detected and located.
 Partial discharge measurement can localize
the damaged part of an insulated system.

1) Test to prove satisfactory operation under ice condition
Under Ice loading condition,
 If the earthing switch/isolator is manually operated, the test may
be considered as satisfactorily completed if the apparatus can be
operated manually, and if it does not, sustain damage (which
may later interfere with its mechanical or electrical performance).
 If the isolator or earthing switch is electrically, pneumatically or
hydraulically operated, the test may be considered as
satisfactorily completed if the apparatus can be operated fully by
the operating device supplied at its rated voltage or pressure, and
if it does not, sustain damage ( which may later interfere with its
mechanical or electrical performance ).

2) Test to prove satisfactory operation at minimum and maximum
ambient temperature
The Isolator or earth switch in the closed position with its operating
devices and auxiliary equipment are placed in a test chamber.
For Minimum Ambient Temp.
The temperature shall be lowered and maintained at the minimum
ambient temperature. The apparatus shall then complete 10 operating
cycles satisfactorily.
For Maximum Ambient Temp.
The temperature shall be raised to and maintained at the maximum
ambient temperature of 40°C. for a period long enough to reach
temperature balance. The apparatus shall then complete 10 operating
cycles satisfactorily.

3) Rotor blocked test
 This test have been conducted for ensuring the proper close
and proper opening of the isolator/Earth switch.
 When the isolator/Earth Switch is perfectly closed then the
operating handle should be locked/blocked with some
arrangement. Similarly for opening of isolator/Earth switch.
 Once the isolator get closed, further movement/rotation of
operating rod are not allowed.

1. Power frequency voltage dry test of the main circuit
 The isolator and Earth switch are subjected to withstand the
power frequency voltage given below for 1 minute.
 The disconnector or earthing switch shall be considered to
have passed the test successfully, if, during the test, no
disruptive discharge occurs.
power frequency
withstand voltage
400KV 220KV 132KV 33KV
Across isolating distance 610KV 530KV 315KV 80KV
To Earth 520KV 460KV 275KV 70KV

2. Voltage tests on control and auxiliary circuits
Auxiliary and control circuits of Isolator and earth switches shall be
subjected to 1 minute power-frequency voltage withstand tests :
 The test voltage of 2000 V is applied to the auxiliary and control
circuits of the Isolator/earth switch. Then there should not be any
disruptive discharge occurs during the test.
 Normally, the test voltage of motors and other devices used in
the auxiliary and control circuits shall be the same as the test
voltage of 2000 V.

3. Measurement of main contact resistance
 The measurement shall be made with DC supply by measuring the
voltage drop or resistance across the terminals of each pole.
4. Mechanical operation test
 With out Voltage/ Current the main contact of isolator/ earth switch
are open or close correctly when there operating devices are
energized. It shall also be verified that operation will not cause any
damage to the isolator/ Earth Switch.
The test shall be carried out:
 At rated supply voltage :- 50 operating cycles
 At specified maximum supply voltage :- 10 operating cycles
 At specified minimum supply voltage :- 10 operating cycles

Type 400KV 220KV 132KV 33KV
1 Main Switch Double end break centre post rotating,
gang operated
2 Service Outdoor
3 Applicable standard IS : 9921 / IEC-62271-102
4 No. of Phases 3 phase
5 Design Ambient temperature 50°C
6 Type of operation Electrically
Ganged
Mechanically
Ganged
7 Rated voltage (kV) In KV In KV In KV In KV
a) Nominal 400 220 132 33
b) Maximum 420 245 145 36

8 Rated current (Amps) 3150 2000 1250 ---
9 Short time current for 3 sec. (KA) 63 40 31.5 25
10 Rated frequency 50 HZ + 5%
11 System earthing Effectively earthed
12 Temperature rise As per relevant IS/IEC standards
13 Lightening Impulse withstand voltage (KVp)
(a) Across Isolating distance 1665 1200 750 195
(b) To earth 1425 1050 650 170
14 1 minute power frequency withstand voltage
a) Across Isolating distance 610 530 315 80
(b) To earth 520 460 275 70

15 Switching Impulse withstand voltage (kVp)
a) Across Isolating distance 1245 530 315 80
b) To earth 1050 460 275 70
16 Max. RIV for frequency between
0.5 MHz and 2 MHz (micro-volt)
1000 at
267kV
1000 at
156kV
500 at
92kV
---
17 Corona Extinction Voltage (kV) 320 156 105 ---
18 Operating mechanism
a) Isolator Motor
b) Earth switch Motor Manual
19 Auxiliary voltage
a) Control & Inter lock 220V DC 80% to 110%
b) Motor voltage 3 Phase 415V AC 50Hz
c) Heater, lamp & socket Single phase 240 V 50HZ

20 Safe duration of overload
a) 150% of rated current 5 minute
b) 120% of rated current 30 minute
21 Minimum creepage distance of
Insulator (25mm/kV )
10500mm 6125mm 3625mm 900mm
22 Mounting structure Tubular Tubular/
Lattice
Lattice Lattice
23 Operating time Less than 12 secs
24 Insulator Data
a) Bending Strength (kgf) 800 800 800 600
b) Height (mm) 3650 2300 1500 508
c) Bottom PCD (mm) 300 254 184 76

24 Bus Bar height from Plinth level
(mm)
8000 5900 4600 3700
25 Phase Spacing (mm) 7000 4500 3000 1500
26 Minimum clearances (mm)
a) Phase to Phase 4000 2100 1300 320
b) Phase to earth 3500 2100 1300 320
c) Sectional clearance 6500 5000 4000 3000

 Grease all the rotating bearings of insulator stack.
 Open the hood on the center rotating post and grease all the sliding
part including the spring studs.
 Clean the contacts and apply white petroleum jelly
 Check the condition of arching horns
 Clean the operating mechanism cubicle
 Check the outgoing connections from the main isolator contacts
and tighten bolts if necessary.

 During annual maintenance it is recommended to measure the
contact resistance of Isolator in on position.
 Use of any type switch cleaning liquid (preferably CRC 2-26 or
Carbon tetra chloride) for cleaning the Aux. contact of Isolator,
Fuse terminals and TB
 Ensure vermin proof arrangement of the Isolator mechanism box
which can prevent entry of insects, reptiles and rats.

 Ensure Aux. AC supply and operation of space heater which
should be available with aux. socket arrangements and door
switched lighting and proper functioning of Ensure Aux. AC
supply and operation of space heater with its thermostat
 Also AC supply must be available with aux. socket
arrangements and door switched lighting.
 In case of saline affected area where possibility of corona is
more, clean Post insulators surface using water or any other
cleaning agent.

A complete live closed circuit must not be opened by
isolator operation and also a live circuit must not be
closed and completed by isolator operation to avoid
huge arcing in between isolator contacts.
As no arc quenching technique is provided in isolator it
must be operated when there is no current flowing
through the circuit. No live circuit should be closed or
open by isolator operation.

IS : 9921
OPTCL Material, “Transmission and Distribution
System”
CPRI material, “Testing & Maintenance of Electrical
Equipment”
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