ats lab

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year Automatic Transfer Switch

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Automatic Transfer Switch "ATS"

Transfer switches allow switching from a primary power source to a secondary

source and are employed in some electrical power distribution systems. Most oftentransfer switches can be seen where emergency power generators are used to back up

power from the utility source. The transfer switch allows switching from utility powerto emergency generator power and vice versa. The switch is either a manual switch or

an automatic switch. During abnormal conditions like power outage in the utility side,

the transfer switches isolate the emergency circuits from the utility and feed it from

the emergency generator. Also, ATS can be used in conditions where the utility is

operating properly, but there is a need for switching the load from the utility side tothe backup generator side, for example during periodic maintenance in utility side.

Figure1: Automatic Transfer Switch Configuration

A transfer switch is set up to provide power to critical loads, which requires

circuit distribution boards to be divided into critical (Emergency) and non-critical(non-emergency) loads. An example of critical loads will be emergency lighting usedin buildings, elevators, healthcare centers & hospitals, control circuits in industrialsystems, computer data servers, fire alarm & fire fighting systems.
http://en.wikipedia.org/wiki/Switcheshttp://en.wikipedia.org/wiki/Emergency_power_systemhttp://en.wikipedia.org/wiki/Electricity_distributionhttp://en.wikipedia.org/wiki/Electricity_distributionhttp://en.wikipedia.org/wiki/Emergency_power_systemhttp://en.wikipedia.org/wiki/Switches

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Types of transfer equipment:

Transfer switches can be categorized into two main groups:

1- Open-transition transfer switch. 2- Closed-transition transfer switch

1-Open-transition transfer switches:

Open-transition transfer switches provide a break-before-make switching action.

The connection to one source is opened before the connection to the second source is

closed. They are specially designed to transfer power between utility and onsitegenerators. Mechanical interlocks that prevent interconnection of sources in automaticand manual modes are commonly used.

Advantages of open-transition transfer systems:

- Lowest-cost automatic power transfer option available, due to the simplicity of thecontrol and mechanism needed, and the simplicity of the interface to the generator

set.

- The open transition ATS panel can be equipped with mechanical interlock thatprevents inadvertent utility paralleling.

Disadvantage of open-transition transfer systems:

- During retransfer from the emergency generator to the utility following restorationof normal power or during maintenance maneuvers, i.e. during switching between2 healthy sources, disconnection of the load is a must (break before make action),

which may not be suitable for some applications and annoying for the operators in

industrial systems.

- During switching action between 2 healthy sources, a fixed open time is needed toallow the arc developed on opening the contacts to decay. Typically this time

requirement is approximately five electrical cycles.

- In applications with motor loads, open-transition transfer switches need to keep theload disconnected for a certain amount of time, from one-half to three seconds, to

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allow the residual voltage present at the motor terminals to decay. This feature is

called programmed transition or delayed transfer.

2-Closed-transition transfer switches:

Closed-transition transfer switches provide a make-before-break switching

action and utilize a momentary paralleling of both sources (

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parallel the sources. This can be very damaging to the power sources or the

transfer equipment.

Due to its complexity and sync-check relay, closed-transition switching

systems are more complex and expensive than open-transition transfer

switches.

Sequence of Operation of ATS

1- Loss of Normal PowerThe control circuit continuously monitors the condition of the primary power

supply. When an abnormal condition is sensed such as power outage, voltage sags,

overvoltage, etc.., a start signal is generated after an adjustable time delay. Onreceipt of this signal, the generator set automatically starts; also, the primary supply

breaker is opened. The generator then accelerates to rated frequency and builds up tothe rated voltage. After reaching the rated voltage and frequency on the generator

supply terminals the generator breaker is closed.

2a- Return of Normal Power (Open Transfer)

When all of the system start signals are removed (i.e. the primary source is

restored), the system will begin retransfer sequence after an adjustable time delay.On completion of the time delay, the generator set transfer breaker will open and,

one second later, the utility (primary supply) transfer breaker will close. Thegenerator set will run unloaded for a cool down period. When the cool down time

delay expires, the unit will shut down and the system will again be ready for

automatic operation.

2b- Return of Normal Power (Closed Transfer)

When normal power is restored, the system will begin retransfer sequence after an

adjustable time delay. On completion of the time delay, the generator bus-bar will

automatically synchronize with the utility service across the utility transfer breaker

using sync-check relay. When the two systems are synchronized, the utility breakerwill close and the generator set will gradually transfer all loads to the utility.

On completion of the load transfer sequence, the generator set transfer breaker will

open. The generator set will run unloaded for a cool down period. When the cooldown time delay expires, the unit will shut down, and the system will again be ready

for automatic operation.

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Figure2: Open Transition transfer sequence from healthy to healthy source

Figure3: Closed Transition transfer sequence from healthy to healthy

source

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Experimental work steps:

1-Determine the components (including specifications forits ratings) required to implement open transition ATSpower and control circuit assuming it will feed a 40Kwatt

inductive load.

2-Draw the control and the power circuit using thecomponents from step 1.

3-Connect the control and power circuit components usingthe wires available in the laboratory.

4-Use the available digital multi meter to test yourconnection.

5-Ask the teaching assistant TA to check your wiringbefore powering up the circuit.

6-Power up the circuit in the presence of the TA, andsimulate utility supply power shut down to check that the

control circuit works as intended from it.

7-Return the utility supply again and see if the controlcircuit returned back to supply the load from the maincontactor path or not.

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Report:

1-Determine the components (including specifications forits ratings) required to implement closed transition ATSpower and control circuit assuming it will feed a (..)

Kwatt electric heaters.

2-Draw the control and the power circuit using thecomponents stated above and illustrate in steps how it

operates.

3- You must write in your report all reasonable assumptionsyou have taken in to your account.

4-Report must be delivered within 2 weeks starting fromyour lab attendance date; it must be delivered hand by

hand.

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Utility

A

A B C

A B C A B C

A B C

A B C

Motor

D.G

Generator

A B C A B C

Voltage

&

Frequency

Monitoring

Relay

Voltage

&Frequency

Monitoring

Relay

C.B.

K2K1

A B C

A B C

Km

220 V

neutral

V.M.R 1

V.M.R 2

.

x

Normally closed contact

Normally open contact

Coil

Indication Lamp

ATS Power Circuit

Legend

T1X K1 K2

V.M.R 1

K2

T1

V.M.R 2

K1

T2

x T2XStart

Open transition ATS

Control Circuit

V.M.R 1If primary supply

is healthy

If 2nd supply

contactor is off

If primary supply

is faulty

If 2nd supply is

healthy

If primary supply

contactor is off

Start

Gen

start

Indication

Lamp

Contactor1

Coil

Contactor2

Coil

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