Electrical Isolator
(Disconnector or Disconnect
Switch)
Introduction
The isolator is a type of switching device and
its main function is to make sure that a circuit
is not completely triggered (to preserve the
circuit).
In other words, we can say that these are
isolation switches used to isolate the circuits.
These switches are applicable in industrial,
distribution of electrical power etc.
They are used in substations to provide the
isolation of equipments like transformers,
circuit breakers.
Usually, the disconnector switch is not
proposed for circuit control but it is for
isolation.
Isolators
are activated either automatically or
manually.
Define an Electrical isolator
The isolator can be defined as a type of
mechanical switch which is used to isolate a
fraction of the electrical circuit when it is required.
Isolator switches are used for opening an electrical
circuit in the no-load condition. It is not proposed
to be opened while current flows through the line.
Generally, these are employed on both the ends of
the circuit breaker, thus the circuit breaker repair
can be done easily without any risk.
Operation of Isolators
In an electrical substation, an electrical isolator
switch is mainly used for disconnecting a power
transformer once it is in a no-load situation or a
little load condition. In full load condition,
isolators don’t operate.
The operation of an isolator can be done
manually or mechanical mechanism from a
remote location. The arrangement of motorized
operation is expensive in comparison to the hand
operation; therefore choice must be taken before
selecting an electrical isolator for the system
which operates manually or mechanically.
145 kV systems used manually operated isolators
whereas,245 kV and 420 kV high voltage
systems used motorized isolators.
Types of Electrical Isolator
The electrical isolators are classified into three
groups on the basis of the system requirement.
They are:
Double Break Type Isolator
(Horizontal Break type Isolator)
Single Break Type Isolator
(Vertical Break type Isolator) (<11 KV)
Pantograph Type Isolator
Double Break Type Isolator
This type of isolator consists of three loads of
post insulators(Post insulator is a high voltage
type of insulators which are designed based on
the IEC,ANSI and other standards).
The middle insulator holds a flat or tubular contact that
can be turned straight by a spin of the middle post
insulator.
The rotation of the middle post insulator can be done
by a lever method at the bottom of the post insulator, as
well as it is related to manual operation (operating
handle) or motorized operation motor (using motor) of
the isolator via a mechanical knot rod.
Opening of double break type isolators
https://www.youtube.com/watch?v=TqLX1Js6Vr4
Single Break Type Isolators
In this type of isolator, arm contact is
separated into two elements. The first arm
contact holds male contact and second arm
contact holds female contact. The arm contact
shifts because of the post insulator rotation
upon which the arm contacts are fixed.
Pantograph Type Isolator
The pantograph type isolator permits current
switchgear installation and it requires the least space.
This type of insulator includes a post insulator as well
as an operating insulator.
Opening and closing of this isolator:
https://www.youtube.com/watch?v=PpwDoPU76D0
All the three isolators:
https://www.youtube.com/watch?v=gSeNoPu0M-s
According to the power system location, the
isolator can be classified into three types namely
bus side, line side and transfer bus side isolator.
Bus Side Isolator is a type of Isolator that
connects by the major bus.
Line Side Isolator stay connected by a feeder
inline side.
Transfer Bus Side Isolator stay connected by
the major bus of a transformer.
Electrical Isolator Operation
The operation of an electrical isolator can be done
by the following two operational methods namely
opening and closing.
1.Opening Operation of Electrical Isolator
Firstly, open the major circuit breaker.
Then divide the load from a system with an
isolator opening.
Close the earth switch. Earth switch can become
an interlock system with an isolator. That’s means
when the isolator is open only that time earth
switch can be closed.
2.Closing Operation of Electrical Isolator
Detach the earth switch.
Shut the isolator.
Shut the circuit breaker.
Difference between Electrical Isolator and Circuit Breaker
The main difference between the isolator and
the circuit breaker is that the isolator detaches
the circuit at the OFF-load situation while the
circuit breaker detaches the circuit at the ON-
load situation.
1.Type of Device
An isolator is an off-load apparatus whereas a
circuit breaker is an ON-load apparatus.
2.Operation
The operation of the isolator is manual whereas
the operation of the circuit breaker is automatic.
3.Device Action
The isolator is a mechanical apparatus that works
like a switch whereas a circuit breaker is an
electronic apparatus made with BJT or MOSFET.
4.Function
When a fault occurs in a substation, the isolator
cuts out a portion of a substation. The other
apparatus works without any intrusion.
The circuit breaker is like an MCB or ACB that
trips the complete system if there is an error
occurs.
5.Withstand Capacity
Isolators have a small withstand capacity when
contrasted to Circuit Breaker.
Circuit breakers have a high withstand capacity at
the condition of ON-load.
Role of Isolator in Transmission Line
Electricalinsulators isolate the transmission
line from the conductor. The isolators are
mainly useful to eliminate grounding loops
like lowering the hazard of accidental lanes for
the flow of current towards the ground.
Maintenance of Electrical Isolators
Electrical isolators suffer from different mechanical
problems, so to overcome this, proper maintenance is
required.
In power systems, isolators are switches where their
opened and closed positions are visible clearly. There
are two essential parts in an isolator like the
insulating part as well as conducting part. So some
actions need to taken for proper maintenance of
isolators from mechanical issues.
We need to clean the insulator body by
removing salt cement as well as acid fumes if
build-up.
If we found any defect, then we have to
replace the isolator with a new one. If the
defect on an isolator is very small, then we can
rub to clean it by using sandpaper. And,
contact rods proper arrangement must be
checked while maintaining.
We must connect the bolts and their connections
like power and earth tightly. Before closing the
isolators, we need to cross-check whether the male
contacts are fitted properly into female contacts or
not, otherwise, we need to adjust.
We need to check the working of the mechanical
interlock by closing the earth switch once the
isolator is closed. If the physical operation is not
possible then we can use the mechanical operation
to rectify it.
Frequently, we need to grease the assembly of
shaft bearing with mechanical connections of
auxiliary switches. We should determine the
contact resistance for every contact of every
phase. For that, we can employ a ‘Digital
Micro Ohm Meter’.
Finally, we must verify the electrical
interlocking method for every isolator.
Electrical Isolator Selection Guide
Electrical isolators operate at no-load conditions,
therefore many factors need to be considered
while selecting isolators include the following:
Voltage level
Rated continuous current carrying capability
Selection of short duration current capacity
Breaker tripping & closing timing
Breaker open & close capacity is also significant
Applications of Isolator
The applications of Isolators involve high
voltage devices such as transformers. These
are protected with a locking system on the
external or with a lock to stop accidental
usage.
Isolator in Substation: When a fault occurs in a
substation, then the isolator cuts out a portion
of a substation.
Thus, this is all about an overview of the
electrical isolator. The characteristics of this
isolator include it is an offload device,
operated manually, De-energize the circuit,
entire isolation for secure maintenance, etc
