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Coming up with a final bill of materials for a complete medium voltage switchgear assembly is an involved task. It takes a qualified individual to analyze the requirements of a system, and review customer specifications and line diagrams of the system.
Fortunately, a significant part of the work has been completed when a manufacturer states that the equipment complies with a certain set of applicable standards. This says a great deal about the equipment.
Also, customers normally provide exact specifications and line diagrams that describe the equipment in detail. System considerations are made and ratings are determined. This task also requires a very knowledgeable individual.
But, a medium voltage switchgear assembly is not a piece of equipment that can be selected from a table. It is a built-to-order product with many details to be considered and many selections to be made. Selecting each component and device to do the job, be acceptable to the customer, and comply with all regional and local standards is quite an undertaking. Every detail, from the electrical and mechanical requirements, down to the finish and composition of the structure must be considered.
The more knowledgeable you are about ANSI and IEC standards, the more valuable you will be to your customer. Become comfortable with reading diagrams that describe a system. They supply a wealth of information about the electrical equipment required, its functioning, and its ratings.
Mini-Specification Guide
Being aware of certain basic information about an assembly that is always required will help to avoid additional questions and lost time. For this reason, a mini-specification guide, covering medium voltage switchgear assemblies is presented for your review.
Use it as a simple guideline when discussing an assembly possibility with your customer.
General Considerations
- What general standards are applicable to the equipment (i.e. ANSI, IEC)?
- Do any special local standards apply?
Ratings
- The switchgear operates on a ____ kV, three-phase, ____ wire, ____ Hz system
- What are the medium voltage circuit breaker ratings?
Main Bus
- The main bus will be of what material and how should it be insulated?
- The main bus will have a continuous current rating of ______ amperes.
- Bus supports should be made from what insulating material?
Circuit Breaker
- What type of interrupting means is the circuit breaker required to use?
- The control voltage for circuit breaker operation will be _____ volts AC (DC).
- What will be the source of control power?
Tripping Means
- What type of protective relaying is required? Single unit microprocessor-based type, or electromagnetic relay types?
Wiring and Terminations
- What is the size and type of the secondary wiring?
- How is secondary wiring to be terminated within the switchgear assembly?
- How will incoming cables be terminated within the switchgear assembly?
Auxiliary Devices
- What are the ratings of required potential (voltage) and/or control power transformers and how are they to be mounted (fixed or drawout)?
Accessory Devices
- Other than standard accessory devices supplied with the switchgear assembly as standard, are any special accessories required, such as:
- Portable circuit breaker lifting device
- Ramp for rolling circuit breaker into lower compartment
- Test cabinet for testing circuit breakers outside the assembly
- Dolly for moving circuit breakers about when outside the assembly
- Electrical levering-in device
Enclosure
- Is the assembly to be indoor or outdoor construction?
- If outdoor construction, what type of construction?
- Outdoor Aisle-less
- Outdoor Sheltered Aisle (or Common Aisle)
- Outdoor Control Room
Finish
- Are there any special finishes, colors or processes required?
Testing
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