POWER CONDITIONER : ISOLATION TRANSFORMER WITH ELECTROSTATIC SHIELDS

DEFINITION:

What is isolation and why is it required?

Galvanic isolation can be defined as high impedance between two electrical circuits to prevent current flow between the circuits yet still allowing information or energy to be exchanged between the circuits by means metallic connections. The heart of isolation is isolation barrier, the impedance is typically exceed 10 ohms.

Why isolate?

First, is for safety protection.

-Safety protection is probably common used because any voltage greater than 60 Volts DC or 30 Volts AC is condired a hazardous voltage. In uses of equipments, it must be protected from such voltages.

Second, Signal level shifting.

-For using transformer either step-up or step down transformer.

Third, Ground disturbance elimination.

-To reduce any high frequency noise to the output.

Why do systems need safety isolation?

The problem of this design is that the controller electronics is the same ground as the end-user. The conrol electronics be damaged especially if they feel short, then end-user is exposed to potentially lethal voltages which can cause damage or death.

Why isolate? …Because safety isolation saves lives

So how do we protect the user against such event?

Well, an isolator is controlling path to isolate the input and the output circuits yet still transmit the necessary control information between the circuits to ensure that the output regulates as designed. With the isolator in placed, a damage short circuit control circuit is block from the end-user. Hence, high voltage path is block because of high impedance between grounds.

Description

It provides galvanic isolation and filter voltage spikes to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected. Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass.

It is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety.

DIAGRAM

Figure I: An example of single shield. The ration of an isolated transformer with electrostatic shield is 1:1. In this example the commercial voltage is equivalent to 120 VAC, and output of 120VAC. The output current is 6.5A according to its specification from the manufacturer. But still we can modify the output current depending on the windings in our transformer.

Figure 2. This indicates that the grounded shield prevents capacitive coupling between primary and secondary windings. With the transformer, as there is no conductive connection between transformer secondary and earth, there is no danger in touching a live part of the circuit while another part of the body is earthed. The Electrostatic shield is made from soft pure copper foil placed between the high voltage and low voltage transformer winding. A copper wire is brazed to the shield and is grounded to the chassis of the transformer.

What is an electrostatic shield?

• The electrostatic shield is simply a grounded single turn of conductive nonferrous foil placed between coils to divert primary noise to ground.The conductive foil completely enclosing the windings will provide a ground path for primary circuit noise and has the advantage that a very much smaller capacitance exists between primary and secondary coils than in the case of a simple Faraday shield.

APPLICATION

Largest end applications:

-Industrial drives & motor control

-Programmable Logic Controllers(PLCs)

-Industrial communications

-Medical electronics

-Power delivery system

SAMPLE IMAGE OF ISOLATED TRANSFORMER

EQUIVALENT DIAGRAM