Electrical interlocks

Electrical interlocking scheme (when the interrupters are manually operated)... 

The preferred way to achieve interlocking between more than one. source of supplies is through electrical schemes only, wherever possible. They are foolproof and can also be operated remotely. Mechanical schemes are generally for smaller installations where, as a result of smaller ratings or cost considerations, a breaker is not used and that imposes a limitation on adopting an electrical interlocking scheme. 

The electrical interlocking should preferably be provided through shunt trip releases. It must have a separate a.c. or d.c. source of control supply, such that the operation of the scheme is independent of the main source of supply. For the same reason, interlocking through undervoltage (U/V) releases is not recommended as its... 

Figure 13.42 Electrical interlocking scheme for manually operated breakers for two sources of supplies...

Electrical interlocking scheme when the interrupters are also electrically operated... 

With shell boilers, economizers will generally only be fitted to boilers using natural gas as the main fuel and then only on larger units. It would be unlikely that a reasonable economic case could be made for boilers of less than 4000kg/hF and A100°C evaporative capacity. The economizer will incorporate a flue gas bypass with isolating dampers to cover for periods when oil is used and for maintenance. The dampers require electric interlocks to the selected fuel. 

The filling method (See Figure 2) is essentially a fail-safe system in that controls are designed to prevent double-cycling. The filling valve and the reservoir valve are electrically interlocked so... 

To ensure correct cooling conditions, the water flow and/or the temperature difference between water outlet and water inlet shall be monitored continuously, acting on an electrical interlock with the motor s power supply, e.g. by intrinsically safe electric circuits. 

The construction of high-voltage starters employs much greater clearances and provides additional safety features such as grounded barriers between the high- and low-voltage sections of the starter. Extensive mechanical and electrical interlocking is also used for additional safety. 

There are chances of explosion or unbumt oil drops going to downstream units if the oil pump continues to supply oil even when air supply pressure at inlet of furnace is too low due to any reason. Electrical interlock of oil pump with manometer indicating air pressure shall be made. The oil pump must stop if air pressure is too low due to any reason (see Fig. 6.5). 

Less/no flow of feed water to boiler—Provision of electrical interlocks for tripping of air blower (and consequently the sulphur feed pump also) when water level is very low in WHRB when there is very less or no flow of feed water to the boiler. 

A form of electrical interlocking for machinery guards which incorporates an actuating switch operated by the guard and associated electronic devices which control power to the equipment. Failure of any of the elements or their connection wiring can be considered a fail to danger arrangement. 

A typical molding cycle will not start until a number of interlock conditions are satisfied. While the interlock conditions vary with the machine, the machine will not enter semiautomatic or automatic mode in the absence of these interlock conditions. Generally, the gate (operator guard door) must be closed and the gate safety (interlock) switches tripped. In hydraulic machines, the front gate has three switches (electrical, mechanical, and hydraulic) whereas the rear gate usually has one or more electrical limit switches. The electrical interlocks are usually electrical limit switches. When tripped, the hydrauHc interlock pre-... 

The U.S. Patent and Trademark Office issued the first patent for an interlock in 1868. The interlock was a mechanical arrangement. The agency issued the first electrical interlock on a power transmission guard in 1923. In 1899, the agency issued a patent for a press guard that prevented the machine from acting if the guard was not fiiUy closed. 

The cask handling crane is provided with mechanical stops and electrical interlocks to prevent its movement near the spent fuel pool after the pool contains irradiated fuel (See CESSAR-DC, Section 9.1.4). 

Feeding arrangement for coal should be given in detail. This may include coal conveyors, crushers, elevators and screwfeeders along with their motor HP electrical interlocks provided and power consumption per MT of steam generated at specified pressure and temperature. 

Electrical interlock of oil pump with air supply pressure at inlet of furnace should be made. The oil pump must stop if air pressure is too low due to any reason. 

Both mechanical and electrical interlocking is used in this technique, depending on the type of machine to be guarded. The system must be designed such that should a fault occur, the guard will fail safely, making the machine inoperable. 

Control functions are meant to ensure that the plant is controlled and kept within its operating envelope under all conditions. At times control functions take certain mitigating actions to lower the demand for protection functions. Interlock is a part of the control system. Interlock systems prevent unsafe conditions or operations, protect personnel, and prevent hazards. Interlocks prevent actions that could lead to or increase danger or damage to the plant, and do not normally initiate actions to correct conditions. Interlocks could be mechanical, administrative, or electrical. The electrical interlock is of interest to this discussion and is part of IAEA guidelines. 

Plastic injection molding machines are very common in many manufacturing plants around the world. Occasionally, the technician needs to reach inside the machine to clear out debris. Many hands and arms have been lost from trying to clean the debris while the machine was still powered on (though not running). An electrical interlock that automatically disconnects the power source when the inside envelope of the machine has been violated is another example of a safety device. 

Check electrical interlocks for proper contact operation. Make sure that each motor is connected to its proper starter. 

Question 7 Does it make a difference how the safety switch on the guard is overridden or if the guard is bolted shut without electrical interlocks that would require the employee to use a tool to remove the door ... 

At the Temelin NPP, disengaging of the suspension or crane hook is avoided by electric interlock of the crane fork pin motion. The engine of the pin drive mechanism is of such dimension that when the pin is loaded, it will not be set into motion. Transport of loads above the reactor and the spent fuel pond is interlocked. Handling is carried out in polar coordinates outside of this restricted area. 

Provide mechanical stops or electrical interlocks to prevent movement of heavy loads over irradiated fuel or in proximity to equipment associated with redundant shutdovim paths. 

Where mechanical stops or electrical interlocks cannot be provided, provide a single-failure-proof crane or perform load drop analyses to demonstrate that unacceptable consequences will not result. 

---