Two Winding Transformer Dimmer, Light Dimmers

Dimmers

• Different lamps/luminaires produce light with constant brightness once they are switched on.
• For the following spots, the variation of brightness of the lamps is required.

For (i) Photo studios (ii) Stage (iii) Drama theatres (iv) Decorations (v) Various functions.

• The device for controlling the brightness is a "Dimmer".
• Dimmer is an electrical and or electronics device. It basically changes the current or voltage which is the cause of varying brightness of luminaries.

  Let us study the circuit arrangements and operation of these dimmers.
1. Variable Resistance Type Dimmer
1.1 Resistance Type Dimmer

1.2 Salt Water Dimmer

2. Dimmer Transformer
In this category there are two transformers

1. Auto transformer dimmer
2. Two winding transformer dimmer

• The dimming can be obtained by varing the voltage applied to the luminary. The variable voltage can be obtained from transformers which are known as dimmer transformers. These are used in theater lighting.
• Explanation of these two types is given below :

2.1 Autotransformer Dimmer

2.2 Two Winding Transformer Dimmer
Types of Two Winding Transformer Dimmer

1. Normal two winding transformer dimmer
2. Coil rotation transformer dimmer

• Let us study the construction and operation of these two types.

2.2 (a) Normal two winding Transformer Dimmer
It is a normal we winding transformer having tappings on the secondary winding.

Circuit Diagram of Normal two winding transformer dimmer

• A tap-changer rotary sector is used to select the tappings.
• So a variable voltage is obtained on secondary to which (L1) (L2)... etc. luminaires are connected.
• Hence tap changer changes the brightness of the lamps.

Application of Normal two winding transformer dimmer

1. Drama stage
2. Theatres

2.2 (b) Coil-rotation Transformer Dimmer

Circuit Diagram of Coil-rotation transformer dimmer

Operation for the system of Coil-rotation Transformer Dimmer

• A motor is used to rotate the winding relative to the fixed secondary winding.
• Due to rotation, the flux linkage between primary and secondary changes.
• When the coil axis are parallel to each other, the flux linkage is maximum. Thus maximum e.m.f. is induced in the secondary coil.
• The luminaries receive maximum voltage and glow bright.
• If the primary coil is rotated such that its axis is 90° to the secondary coil, the flux linkage is minimum.
• Thus minimum e.m.f. is induced in the secondary coil.
• The luminaries receive minimum voltage and glow dim. For the angular positions between 0° to 90°, the brightness increases gradually.
• The motorized set can be operated through remote control. Since primary is a rotating member, the current is fed through flexible connections as shown.

Application of Coil-rotation Transformer Dimmer

1. Stage
2. Theatres.

3. Electronic Dimmer

3.1 Thyristor operated dimmer

3.2 Triac Operates Dimmer