Introduction to Electrical Transformer

Introduction to Electrical Transformer

What is a Transformer?

In Very Simple words.

Transformer is a device which:

1. Transfer Electrical power from one electrical circuit to another Electrical circuit.
2. It’s working without changing the frequency.
3. Work through on electric induction.
4. When, both circuits take effect of mutual induction.
5. Can’t step up or step down the level of DC voltage or DC Current.
6. Can step up or step down the level of AC voltage or AC Current.

• Without transformers the electrical energy generated at generating stations won’t probably be sufficient enough to power up a city. Just imagine that there are no transformers.How many power plants do you think have to be set up in order to power up a city? It’s not easy to set up a power plant. It is expensive.
• Numerous power plant have to be set up in order to have sufficient power. Transformers help by amplifying the Transformer output (stepping up or down the level of voltage or current).
• When the number of turns of the secondary coil is greater than that of primary coil, such a transformer is known as step up transformer.
• Likewise when the number of turns of coil of primary coil is greater than that of secondary transformer, such a transformer is known as step down transformer.

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Degradation of Insulation in Switchgear (What’s Really Happening)

Partial Discharge

Partial Discharge (PD)

Electrical insulation is subjected to electrical and mechanical stress, elevated temperature and temperature variations, and environmental conditions especially for outdoor applications. In addition to normal operating conditions, there are a host of other factors that may trigger accelerated aging or deterioration of insulation.

Switching and lightning surges can start ionization in an already stressed area. Mechanical strikes during breaker operation can cause micro cracks and voids. Excessive moisture or chemical contamination of the surface can cause tracking. Any defects in design and manufacturing are also worth mentioning.

Partial Descharge

PD is a localized electrical discharge that does not completely bridge the electrodes. PD is a leading indicator of an insulation problem. Quickly accelerating PD activity can result in a complete insulation failure.

PD mechanism can be different depending on how and where the sparking occurs:

• Voids and cavities are filled with air in poorly cast current transformers, voltage transformers and epoxy spacers. Since air has lower permittivity than insulation material, an enhanced electric field forces the voids to flash-over, causing PD. Energy dissipated during repetitive PD will carbonize and weaken the insulation.
• Contaminants or moisture on the insulation induce the electrical tracking or surface PD. Continuous tracking will grow into a complete surface flash-over.
• Corona discharge from sharp edge of a HV conductor is another type of PD. It produces ozone that aggressively attacks insulation and also facilitates flashover during periods of overvoltage.

Features of partial discharge activity, such as intensity, maximum magnitude, pulse rate, long-term trend, are important indications of the insulation’s condition.

Healthy switchgear has very little or no PD activity. If PD activity is significant, it will eventually deteriorate insulation to a complete failure. Higher voltages produce higher intensity partial discharges, thus PD detection in gear with higher voltages (13.8 kV and up) is more critical.

Possible locations of partial discharge in switchgear:

1. Main bus insulation
2. Circuit breaker insulation
3. Current transformers
4. Voltage transformers
5. Cable terminations
6. Support insulators
7. Non-shielded cables in contact with other phases or ground

 

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The Switchboard Design Requirements

Switchboard Panel

The Switchboard Design Requirements

Design Rules

The following rules of design have to be implement in the aim to facilitate the assembly and especially the maintenance of the installation.

The switchboard must be designed the way to have a clearly visible separation between the 3 following zones:

• One dedicated for the devices installation
• One dedicated for the bus bars mounting
• and one dedicated for the out-goers cables connections 

Switchboard Areas

The goal of that architecture is to separate the switchboard in different areas in function of each professional user.

• Devices zone => panel builder and exploiter
• Bus bars zone => panel builder
• Cable connection zone => installer and maintenance

In order to facilitate the access within the switchboard for the maintenance, its covering panels must be dis-mountable on all surfaces for any IP degree.

All the devices must be installed onto dedicated mounting plate designed for one or several switchgear of the same type. The objective of that point is to regroup the protection equipment of the same nature each others and distinguish inside the switchboard the function of each device or group of devices.

Theses mounting plates will have an independent fixing system affording them to be transformed and moved anywhere in the switchboard and especially to make it easier the installation evolution.

To insure the maximum protection of people around the electrical installation, front plates must be installed in front of all control and protection equipment in order to avoid a direct access without a tool to the devices and consequently to the active parts.

For safety reasons and especially when the door will be opened during the switchboard working, all bus bars have to be covered by barriers onto the whole perimeter of the bus bars zone.

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