Protection Relays

In electrical engineering, a protective relay is a complex electromechanical apparatus, often with more than one coil, designed to calculate operating conditions on an electrical circuit and trip circuit breakers when a fault is detected. Unlike switching type relays with fixed and usually ill-defined operating voltage thresholds and operating times, protective relays have well-established, selectable, time/current (or other operating parameter) curves.

Such relays may be elaborate, using arrays of induction disks, shaded-pole magnets, operating and restraint coils, solenoid-type operators, telephone-relay contacts, and phase-shifting networks. Protection relays respond to such conditions as over-current, over-voltage, reverse power flow, over- and under- frequency. Distance relays trip for faults up to a certain distance away from a substation but not beyond that point. An important transmission line or generator unit will have cubicles dedicated to protection, with many individual electromechanical devices.

The various protective functions available on a given relay are denoted by standard ANSI Device Numbers. For example, a relay including function 51 would be a timed overcurrent protective relay. Design and theory of these protective devices is an important part of the education of an electrical engineer who specializes in power systems. Today these devices are nearly entirely replaced with microprocessor-based digital protective relays (numerical relays) that emulate their electromechanical ancestors with great precision and convenience in application.

By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays. However, due to their very long life span, tens of thousands of these "silent sentinels" are still protecting transmission lines and electrical apparatus all over the world.

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How to Change Spark Plugs

The humble spark plug has changed very little over the years—and changing them is as simple as ever.

To complete this How-To you will need:

A vehicle owner's manual
New spark plugs
A socket wrench
A spark plug socket
A socket wrench swivel joint
And a socket wrench extension
A spark plug wire puller
A cleaning rag
And rubbing alcohol

Step 1: Let car cool down

Park your car and wait for it to cool down. This may take a few hours, since the spark plugs are among the hottest parts of your engine.

Step 2: Locate spark plugs

Pop open the hood and locate your spark plugs by referring to your owner's manual.

Step 3: Remove one spark plug

Remove one spark plug wire from the end of the row by pulling its boot, or the little cap where it connects to the engine—not by yanking on the wire itself.

Tip: You can also use a spark plug wire puller to easily detach the wire.

Step 4: Attach spark plug to socket wrench

Attach the spark plug socket to the socket wrench. You may need to use a swivel joint and/or a socket wrench extension to reach the spark plug.

Step 5: Remove spark plug

Remove the spark plug by turning the socket wrench counterclockwise.

Step 6: Make sure hole's clean

Make sure that the spark plug hole is clean. If necessary, use a rag and rubbing alcohol or compressed air to clean the spark plug hole.

Step 7: Install new spark plug

Carefully install a new spark plug into the empty hole and tighten it by hand.

Step 8: Secure new spark plug

Use the socket wrench to secure the new spark plug in place.

Step 9: Reconnect spark plug wire

Reconnect the spark plug wire onto the new spark plug.

Tip: Changing your spark plugs one at a time prevents incorrect installation that can affect the car's timing and engine performance.

Step 10: Move on to next spark plug

When you have successfully changed a spark plug, move on to the next one until you have finished installing all new plugs.

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The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites.


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What is an actuator?

motor actuator

An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which an agent acts upon an environment. The agent can be either an artificial intelligence agent or any other autonomous being (human, other animal, etc).

source: wikipedia

An actuator is something that converts energy into motion. It also can be used to apply a force. An actuator typically is a mechanical device that takes energy — usually energy that is created by air, electricity or liquid — and converts it into some kind of motion. That motion can be in virtually any form, such as blocking, clamping or ejecting. Actuators typically are used in manufacturing or industrial applications and might be used in devices such as motors, pumps, switches and valves.

source: wisegeek.com