Reliable electrical power becomes one of the most wanted factor in modern world industry where operation should be uninterruptible and maximize the cycle of operation, output quality and to avoid losses and damages. Here we are talking about Automatic Transfer Switches (ATS) also known as Automatic Mains Failure (AMF) panel to cater uninterrupted power supply from Mains or backup sources like Diesel gen-set, static ups etc.
What is Automatic Transfer Switch (ATS)?Automatic Transfer Switch (ATS) is an automated switching device that transfers load power to backup power during mains failure and back to its original state when mains power reinstate to the normal condition. It will have its own contacts, microprocessor to analyses the conditions whether power supply is normal or backup and need backup or mains power. Here "back up power" may become either Standby generator or another mains power or static power source like UPS.
Automatic Transfer Switches (ATS) OR Automatic Mains Failure (AMF) Panel
Provide and install automatic transfer & bypass-isolation switch (ATS / BPS) system(s) with number of poles, current rating, voltage, withstand and close-on ratings as required by the system. Each automatic transfer shall consist of an inherently double throw power transfer switch mechanism and a microprocessor controller to provide automatic operation. All automatic transfer & bypass-isolation switches and controllers shall be the products of the same manufacturer. These switches shall be separate cubicle mounted and located as shown on the relevant drawing. Coordinate with the requirements of the rating as shown on the LV schematics.
Coordinate the incoming and outgoing maximum ampere ratings required to serve the load, complete with the following features and characteristics. Provide necessary equipment and interconnection wiring to ensure proper functioning of controls in accomplishing the sequence of operation outlined herein and with the transfer switch accessories outlined. Note change over ACB / MCCB shall not be accepted.
Included Components and Functions with ATS / AMF
- Full Relay Protection for 3-Ph, 4-wire System. Transfer to emergency source when voltage on any phase drops to 70 percent or less. Re-transfer to normal when all phase voltages are 90 percent or more.
- Adjustable time delay on generator start sequence, 10 seconds maximum, in all second intervals.
- Adjustable time delay on automatic transfer to normal, 15 to 30 minutes in 1 minute intervals. If the emergency source fails and power is available from the normal source, the time delay shall be defeated and the transfer operation immediately initiated.
- Two normally open and two normally closed auxiliary contacts on main shaft.
- Mounted pilot light to indicate switch in normal position.
- Mounted pilot light to indicate switch in emergency position.
- Engine Starting Contacts.
- Test switch and necessary equipment for remote test switch.
- Under-frequency Relay.
- Other Controls as necessary for the smooth automatic function of the system.
Switched Neutral Contacts
The neutral of the normal and emergency power sources shall be switched through a fourth pole of the transfer switch which shall be non-overlapping (break before make) and shall operate with the main poles of the switch.
In-Phase Monitor Control
The transfer switch shall include an in phase monitor to protect against abnormal inrush currents, which may result from out-of-phase transfer of motor loads. The monitor shall initiate operation of the transfer switch when the remote or local push-button is actuated and the phase angle between both sources is approaching zero phase angle. The motor currents upon re-connection shall not exceed normal starting values. In-phase transfer shall be provided in either direction whenever both power sources are above 70% of nominal voltage.
The in-phase monitor shall incorporate silicon semiconductor control logic and an industrial grade output relay, rated for operation of the transfer switch. The in-phase monitor shall be automatic transfer switch.
Sequence of ATS / AMF Operation
- The transfer switch shall be interlocked to provide the operation specified herein. ln addition to those specified herein, all relays and sensing devices shall be provided to accomplish the functions.
- When normal power fails on the transfer switch (adjustable time delay relay set at 1 to 2 seconds) the engine-generator starting sequence shall be initiated.
- When emergency power is available at the transfer switch that indicates failure of normal power, the transfer switch shall transfer without delay. Voltage and frequency relay settings as required.
- The ATS/BPS shall be tested in accordance with BSEN-6-497-6-1 and be labelled accordingly. Type test certificates from a recognised test laboratory shall be provided.
Tests and Certification
The complete ATS / BPS shall be factory tested to ensure proper operation of the individual components and correct overall sequence of operation and to ensure that the operating transfer time, voltage, frequency and time delay settings are in compliance with the specification requirements.
Upon request, the manufacturer shall provide factory test certificates certifying compliance with all of the requirements of this specification including compliance with the above codes and standards, and withstand and closing ratings. The certification shall identify, by serial number(s), the equipment involved. No exceptions to the specifications, other than those stipulated at the time of the submittal, shall be included in the certification.
The ATS / BPS manufacturer shall be certified to ISO 9001 international Quality Standard and the manufacturer shall have third party certification verifying quality assurance in design / development, production, installation and servicing in accordance with ISO 9001.
The ATS / BPS manufacturer shall maintain a national service organization of company- employed personnel located throughout the country. The service center's personnel must be factory trained and must be on call 24 hours a day, 365 days a year. The manufacturer shall maintain records of each switch, by serial number, for a minimum of 20 years.
Monitoring And Controls of ATS / AMF
Provide monitoring / recording instruments and meters as required by BMS. Install in each switchboard and control panel all necessary transducers, current transformers, sensors and other accessories required for remote control and operation by the local control network and the BMS.
The switchboard manufacturer shall allow sufficient space and accessibility for such equipment and also provide wiring and terminals sufficient in number and adequate capacity for the field wiring.
Last Modified: 08-Nov-2018