Can transformers be used in parallel?

Figure: Transformers in Parallel

Single phase transformers can be used in parallel only when their impedances and voltages are equal. If unequal voltages are used, a circulating current exists in the closed network between the two transformers, which will cause excessive heating and result in a shorter life of the transformer. In addition, impedance values of each transformer must be within 7.5% of each other. For example: Transformer A has an impedance of 4%, transformer B which is to be parallel to A must have an impedance between the limits of 3.7% and 4.3%. When paralleling three phase transformers, the same precautions must be observed as listed above, plus the angular displacement and phasing between the two transformers must be identical.

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What is the difference between Electric Motor and Electric Generator?

Figure-1: Generator

Figure-2: Motor

Difference between Electric Motor and Electric Generator: 

• A generator converts mechanical energy into electrical energy, while motor converts mechanical energy into electrical energy. 
• In a generator, a shaft attached to the rotor is driven by a mechanical force and electric current is produced in the armature windings, while the shaft of a motor is driven by the magnetic forces developed between the armature and field; current has to be supplied to the armature winding. 
• Motors (generally a moving charge in a magnetic field) obey Fleming`s left-hand rule, while the generator obeys Fleming’s right-hand rule.

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Describe a Starter-Motor Circuit.

Figure 1: Typical Starter-Motor Circuit.

A Starter-Motor Circuit: 

Figure 1 shows a very simple diagram of an engine starter-motor circuit. If one day you turn on the ignition switch, push the start button, and nothing happens, this is the circuit diagram you will need. A complete engine wiring diagram would probably contain the same information, but it would also contain all of the meters, idiot lights, and alternator wiring, adding considerable visual confusion.

For the starter-motor circuit all you need to see are the:

• Battery switch 
• Fuse between battery switch common terminal and engine panel 
• On/Off switch 
• Momentary start switch
• Wire from starting switch to solenoid 
• Heavy positive cable from battery-select common terminal to solenoid 
• Heavy negative cable from battery negative terminal to engine negative terminal. 

If the engine won’t turn over, the problem probably lies somewhere in this diagram.

Source: Boatowner's Illustrated Electrical Handbook

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What is the difference between Electric Motor and Electric Generator?

Difference between Electric Motor and Electric Generator: 

• A generator converts mechanical energy to electrical energy, while motor converts mechanical energy to electrical energy. 
• In a generator, a shaft attached to the rotor is driven by a mechanical force and electric current is produced in the armature windings, while the shaft of a motor is driven by the magnetic forces developed between the armature and field; current has to be supplied to the armature winding. 
• Motors (generally a moving charge in a magnetic field) obey Fleming`s left-hand rule, while the generator obeys Fleming’s right-hand rule. 

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What is RMU (Ring Main Unit) and Its Use in Electrical Power Distribution System?

Ring Main Unit (RMU) is a 11 KV or 33 KV HT panel having 3 nos. of switches (Circuit Breakers or Isolators or LBS) that are 2 for incoming one for outgoing. It enables consumer use 2 sources of HT power in at the same metering point. It is a totally sealed, gas-insulated compact switchgear unit.

RMU is to be used two incoming with mechanical or electrical interlock and one out going  to the load generally but some times one incoming and two outgoings medium voltage supplies. In engineering distribution this is called flexible power supply. Now a day SF6 (Sulfer Hexa-Floride) circuit breakers going to be used. These are maintenance free breakers. 

Figure 1 – Outlook of a typical three-feeder 24 kV RMU unit

Figure 2- 11 KV 2 Incoming and 3 Outgoing RMU at Bangladesh Film Archive.

Ring Main Unit is used in a secondary distribution system. It is basically used for an uninterrupted power supply. Alongside, it also protects your secondary side transformer from the occasional transient currents. 

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