ALARM EQUIPMENT DETAILS FOR HV & EHV POWER TRANSMISSION SYSTEM

Fig: Fire drill in an airport

Alarm Equipment Associate with Power Control Panel in Transmission Grid Station

Where an alarm system is specified in this article, especially for High Voltage transmission grid and normal Voltage Distribution substation, it should consist of an initiating device, a display unit, and push buttons mounted on the front of the appropriate control panel, together with a continuously rated audible warning device flasher unit and relays. The relays should wherever possible, be mounted inside the same panel; where the number of alarms to be displayed makes this impracticable, a separate alarm relay cubicle or cubicles will be considered as an alternative.

Multiple Alarm Tone

Where it is necessary to differentiate between the urgency of alarms then various approved alarm tone devices should be provided in this Contract. In addition and where specified an alarm beacon to the approval of the Engineer should be provided.

Specification of Alarm Display Unit

The display unit should consist of a rectangular frame or bezel enclosing the required number of individual fasciae, each of which should be preferably approximately 32mm x 25mm in size. Each fascia should be in a window inscribed with the specified legend, describing the fault condition to be indicated. Lamps should not illuminate adjacent windows.

At least 3 spare ways should be provided on each display unit. All unused ways in a display unit should be fully equipped and the alarm system designed to enable these ways to be utilized at a future date.

Alarm Accessories Specification and Setup

Alarm relays should be of a type to the approval of the Engineer, arranged to plug into fixed bases, either singly or in groups, and have positive means of retaining them securely in the service position, the bases being mounted on racks or frames which should be hinged to allow them to be swung clear of the sides of the panel or cubicle in which they are installed in order to provide ready access.

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Alarm Accessories Wiring Procedure

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The type of wiring used for internal connections between alarm fasciae and their relays and between relays and terminal blocks should generally comply with these requirements with the following exceptions:

(i) Single-strand wire, not less than 0.85 mm in diameter may be used.(ii)Soldered terminations will be acceptable.

External connections for alarm circuits will in general be run in multi-core cables having a larger core size than that referred to above. This will necessitate special terminal blocks if soldered terminations are used, in which case the internal and external terminations of each pair should be joined by a removable link. Samples of the type of wire and terminal block for alarm connections should be submitted for the Engineer’s approval.

 

Alarm Operation System

The operation of the alarm system should be as follows:-

(i) When an external alarm indicating contact closes the audible warning should sound continuously and the appropriate fascia should be illuminated by a flashing light at a frequency which allows the inscription to be easily road.

An Accept push-button should be provided on or near the display unit, which when pressed, should silence the audible signal and cause the fascia to remain illuminated steadily.

The alarm circuit should be designed to retain the indication after the re-opening of the initiating contact, requiring a separate Reset push button to be pressed before the alarm is canceled.

A Test push button should be fitted close to the Accept and Reset buttons, to illuminate all the fasciae on the associated display unit for as long as the Test button is depressed.

The operation of the Accept button should not preclude the receipt of further indications giving more audible alarm and visual indications as the result of the operation of other sets of alarm contacts.

Alarm System Relay Setup for Power Grid Control Panel

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High Voltage transmission and normal Voltage Distribution network control panel alarm systems must be in such a way that relays should not be continuously energized when the alarm system is at rest.

For all alarm indication initiating devices a spare set of voltage-free contacts should be provided- this may be by the use of auxiliary relays, and connected by cable to a suitable, approved marshaling cubicle. These spare contacts will provide for the transmission of the alarm indication signals to the remote GCC- Grid Control Centre.

The Service provider should be responsible for providing all the alarms required for the safe and efficient operation of the Substation. General descriptions of alarm requirements are given in the specification and the Service provider should include any other alarms that are necessary due to the type of equipment and design of the plant to the engineer’s approval.