Electrical measuring, testing and protection instruments

1. R.M.KCOLLEGEOF ENGINEERINGANDTECHNOLOGY

3. 1. Appliance tester
2. Battery testers
3. Cable fault testers
4. Continuity testers
5. Dry block calibrators
6. EMF meters
7. Flow switches
8. Ground resistance meters
9. High pot testers
10. ISE meters
11. LCR meters
12. Megohmmeter
13. Phasing testers
14. Volt stick pen etc………
Let us discuss a few of the above mentioned instruments in a brief note :-

4. MEGGER
 Megger is an instrument used to measure the insulation resistance of a system or
an equipment.
 It is being used since 1889 and become popular in 1920,s.
 IR of a system or an equipment degrades due to various environmental factors such
as temperature ,humidity, moisture as well as due to mechanical and electrical
stresses.
 We are supposed to give DC supply to the megger either from the battery or some
Other converters.
 The device enables us to measure electrical leakage in a wire.
 It is mostly used for verifying the electrical insulation level of any device such as
Motor, generator windings, cable etc..
 It not only measures the insulation resistance but also it shows us the exact area of l
Electrical puncture.

5.  Meggers can be broadly classified as :-
1. Electronic type megger,
2. Hand operated megger.
(Megger contd.)

6. VOLT STICK PEN
 A volt stick pen is the one that resembles a pen which is used to detect power in a
circuit or a conductor.
 The tip of the pen should be bring in contact with a wire, socket, terminal outlet or
somewhere else where we need to detect the presence of power.
 If the tip of the pen glows red along with a beep sound, it indicates the presence of
power supply.
 It is more convenient to use in the residential and office
wirings where a clamp meter is difficult to be employed
in order to check whether any internal wiring gets failed.
 It senses the electrical field around the conductor and gives
the output unlike the concept of letgo currents in a normal
electrical tester in which we need to make our finger contact
with the metallic tip.

7. CLAMP METER
 A clamp meter or a current probe is a current measuring device with jaws which
open to allow clamping around an electrical conductor.
 This allows the measurement of current in a conductor without the need to make
any physical contact with the wire.
 AC clamp meters that measures only ac current works on the principle of current
transformer where the wire acts as a primary winding and the clamp acts as a
secondary winding.
 Hence, by the principle of electromagnetic induction, it gives the magnitude of the
current that is flowing in the circuit.
 Since the alternating current frequently reverses polarity, the Dynamic
fluctuations in the magnetic field which are proportional to the current flow in the
wire.
 DC clamp meters works on the principle of hall effect.

8.  Hall effect sensors sense the magnetic field caused by the current flow which causes
a small voltage across the hall effect sensor.
 Clamp meters often includes other sensors such as voltmeters, ohmmeters etc..
which increases the versatility of the instruments.

9. BATTERY TESTER
 A battery tester is an electronic device intended for testing the state of an electric
battery, going from a simple device for testing the charge actually present in the cells
and /or its voltage output, to a more comprehensive testing of the battery’s condition,
namely its capacity for accumulating charge and any possible flaws affecting the
battery’s performance and life.
 Substations and other receiving stations employs a set of battery banks that are needed
to be tested frequently as a part of maintenance.
 Working :
The most rudimentary battery testers, those found on battery packages, use
a conductive ink that responds to minute temperature changes. If a battery
has a charge, the ink heats up as the current passes through it. If the
temperature is higher, the battery has more current.

10. Underground cable fault distance locator
 Almost all the metropolitan cities have equipped with underground cables
completely for electric power distribution and hence it is a great challenge for
the electrical engineers to give a reliable and continuous power supply without any
outages.
 The task of locating the cable, trace of the path and finally detecting the fault needs
skilled personnel.

11. Continuity tester
 A continuity tester is an item of electrical test equipment used to determine if an
electric path can be established between two points; that is if an electric circuit
can be made.
 The circuit under test is completely deenergised prior to connecting the apparatus.
 A continuity tester consists of a battery in a housing, with test probe connected to
one end of the battery housing and a test wire with an alligator clip connected to
the other end.
 It is also used to determine whether a particular electric component is carrying
electricity and to pinpoint the cause of a problem.
 If the circuit is continuous or a component is carrying current, then the tester glows
and gives a beep sound.

12. To use a continuity tester, unplug the appliance and disassemble it to get at the
component you want to test. Fasten the clip of the tester to one wire or
connection of the component, and touch the probe to the other wire or
connection. If the component is receiving electricity and transmitting it, the tester
will light or buzz; this indicates that the circuit is continuous. If the tester doesn't
light or buzz or it reacts only slightly, the component is faulty.

13. SURGE PROTECTION DEVICE
 A surge protector (or surge suppressor or surge diverter) is an appliance or
device designed to protect electrical devices from voltage spikes. A surge protector
attempts to limit the voltage supplied to an electric device by either blocking or
shorting to ground any unwanted voltages above a safe threshold.
 Today’s residential, commercial and industrial set-ups are heavily reliant on
the continuous and efficient running of electrical and electronic systems. Over-
voltage surges are a major cause of failure of these equipment. Such transient
over-voltage surges are often generated due to direct/indirect effects of
lightning strikes, switching of utility grid or capacitor banks, electrical
accidents, turning on/off of nearby heavy load machines, AC chillers, motors,
pumps, circuit-breaker tripping etc. Surges can cause destruction of electronic
circuitry components, logic failures and breakdowns. Loss of operation, loss of
service, loss of data, and loss of production can be huge and by far higher than
the cost of damaged equipment. Long term exposure to lower level transient
over-voltages can also lead to premature ageing of equipment.

14. Circuit diagram :
They are mostly employed in power distribution panels, process control systems,
communication systems and other heavy industrial machine control panels.

15. Some other protection equipments used in industries and substations are as follows :
1. Earth leakage circuit breaker(ELCB) :
2. Residual current circuit breaker :
An Earth-leakage circuit breaker (ELCB)
is a safety device used in electrical
installations with high Earth impedance to
prevent shock. It detects small stray voltages
on the metal enclosures of electrical
equipment, and interrupts the circuit if a
dangerous voltage is detected. Once widely
used, more recent installations instead use
residual current circuit breakers which
instead detect leakage current directly.
The main intention of the RCCB Is to break
an electric circuit instantly In order to save a
person from ongoing Electrical shock.

16.  Instrument transformers
 Isolators
 Air and vaccum CB’s
 Lightning arrestors
 Protective relyas etc…..
CONCLUSION :
 Apart from what we have discussed till now, there are still large number of
instruments that we employ in various applications such as energy auditing.
 In order to have a continuous and reliable power supply, the measuring and
testing instruments as well as the protection instruments plays an outstanding role.
 Hence it is very important for an electrical engineer to have a basic knowledge
over this.