Substation Design 1

List the five general design goals that should be considered when designing a substation.

Safe, reliable, versatile, expandable and cost-effective.

List the seven environmental considerations that must be taken into account when designing a substation.

Electromagnetic fields, seismic criteria, altitude effects, lighting considerations, audible noise, wetlands and waterways and aesthetic and area impact.

List the major steps of the substation design sequence, in chronological order.

Site design, Major equipment selection, structure design, foundation design, grounding design, bill of material and assembly of work order documents.

Explain why a fault on a substation radial bus results in the complete de-energization of the bus.

The feeder breaker should trip to clear the fault without interrupting any other loads.

Explain what the inverse time-current characteristics means as applied to protect devices.

That slight overcurrent conditions will be allowed to persist longer than large overcurrent conditions.

Explain why maintaining the voltage within tolerance is challenging to the provider.

As load increases, so does current and consequently voltage drop.

What does an insulation system's BIL value represent?

Represents the "strength" of the insulation for a high-voltage impulse similar to a lighting strike or switching surge.

Explain how an imaginary sphere rolling up and over a substation gives protection from a direct lighting strike.

As long as the sphere us touching two grounded points, equipment under the sphere is considered to be protected from a direct strike.

List the three basic types of graded yards.

Flat, sloped or stepped.

What three factors must be considered when providing for adequate drainage for a substation yard?

The type of soil, the amount of rainwater that will percolate into the ground, the amount of rainwater that will become runoff.

what two types of conductor can be used in a substation ground grid to deter theft?

Copper clad and aluminum clad steel.

When constructing a substation ground grid, ground rods are most effective if they __________.

Reach the water table

It is critical that a substation ground grid be well designed to minimize the _______ to personnel working in or around a substation.

step and touch potential

The range of current magnitudes that will cause ventricular fibrillation, measured in milliamps is ________.

60-100 mA

What two factors determine the size of the conductors for the substation ground grid?

Must be sized to carry anticipated fault current without fusing or melting.

Explain some of the costs that must be considered when ordering a substation power transformer.

initial costs and operating costs in the form of no-load losses and load losses. Measured in watts.

What is the fault interrupting speed of typical distribution substation circuit breaker?

3 or 5 cycles

Where is the highest seismic hazard area in the united states?

West coast

What does the acronym NIMBY (not in my back yard) refer to when selecting a new substation site?

Physical appearance of utility facilities

All devices between the distribution bus and the distribution feeder must have a ___________ sufficient to serve the highest load that will be supplied by the feeder.

Rating

If the federal government is involved in selecting a substation site, a(n) _________ must be submitted and evaluated.

Environmental impact statement

The legal description of the substation site is given in the ________.

General layout

Which type of drawing is an electrical representation of the equipment installed in a substation?

One-line drawing

Why does a fault on a substation radial bus result in the complete de-energization of the bus?

every breaker must trip to isolate the fault

Which of the bus configuration is quite common, particularly at 230 kV and above?

Breaker and a half

True or false: An inverse time-current characteristics means that slight overcurrent conditions will be allowed to persist longer than larger overcurrent conditions.

True

In most cases, some means of voltage regulation is required to maintain a + or - ______% voltage tolerance.

5%

What does an insulation system BIL value represent?

Basic impulse level

In one method of shielding against lighting, as long as the _________is touching two grounded points, equipment under it is protected from direct strike.

Sphere used on 230kV and above subs

which of the following is one factor that must be considered when providing for adequate drainage of a substation yard?

Soil type

When planning a substation access road, what must the designer account for?

Size and weight of vehicles

What is one design tactic for a substation security fence to help keep people safe?

Place it 3 ft inside the property line to ensure the ground grid can extend outside the fence.

What types of conductors can be used in a substation ground grid to deter theft?

Traceable conductor

when constructing a substation ground grid, ground rods are most effective if they are _________.

Driven deep enough to reach low-resistance soil

True or false: Minimizing the step and touch potential hazards around a substation begins with a well-designed ground grid.

True

The range of current magnitudes (measured in milliamps) that will cause ventricular fibrillation is _____.

60-100 mA

What determines the size of the conductors for the substation ground grid?

Available fault currents

True or false: Costs need not be considered when ordering a substation power transformer.

False

What is the fault interrupting speed of a typical distribution substation circuit breaker?

3 or 5 cycles

Why are capacitor banks often installed in substations?

To correct the power factor

Who dictates how much water must be confined to the site and how much (if any) is allowed to leave the site?

Local regulations

True or False: voltage regulators have a typical range of plus or minus 10% of the applied voltage.

True

What is the fault interrupting speed of a transmission circuit breaker?

2 or 3 cycles

What's are the major components of a switching station?

Circuit breakers

what is the purpose of the distribution substation?

To supply power to the feeder system, which in turn, delivers power to the load or utility customers.

At what elevation above sea level do changes must be made to the substation design to account for the physical properties of the high-altitude air?

5000 ft or more above sea level

What is a environmental impact statement?

reports that outline the predicted environmental effects of a particular action or project in which the federal government is involved.

What does UBC stand for?

Uniform Building Code, its a set of regulations covering all major aspects of building design and construction relating to fire, life safety and structural integrity.

What does the rock layer help reduce?

It increases the resistance, thus reducing the current seen in both step and touch potentials.

What does the grand plan show?

It indicates the size of the conductors used in the grid and the number and type of ground rods to be driven at each location.

What views does the electrical layout give you?

Gives both plan (top) views and elevation (side) views with all the details necessary for the installation equipment.

What is the bill of material?

It list every piece of material used in the construction of the substation.

How can the reliability of the radial bus be improved?

By adding a second source configured in a ring bus.

What happens when one breaker in the ring is opened?

All circuits leaving the ring bus remain energized but the reliability of the ring is compromised.

When is the double bus arrangement used?

In situations where extremely high reliability is essential.

True or false: double bus is the only topology where a breaker failure condition never results in the loss of an undulated element.

True

At what voltages is the double bus and breaker and a half topologies used?

At 161 kV and above

what is a fast transfer?

Involves opening the first source breaker and then closing the second breaker very quickly.

What drives the paper insulation to continuously undergo a chemical breakdown?

heat and oxygen

True or false: In a transformer, the short circuit does not have to occur inside the transformer to be damaging.

True

What is the basic theory behind a differential relay?

Whatever goes in should come out.

At distribution voltages, what can be used instead of SF6 interrupters>

Vacuum interrupturs.

Under normal conditions, voltage at the delivery point must be maintained at what voltages?

35% of nominal

What is the advantage when using voltage regulators instead of LTCs?

The ability to control the sending end voltage of each feeder individually.

What is basic impulse level sometimes referred to?

Basic insulation level, also helps achieve proper insulation coordination.

What IEEE standard contain the guide for containment and control of oil spills in substations?

980

What resistance does the rock selected need to have?

At least 3000 ohm-meters whether wet or dry.

Where can substations be built indoors?

In dense urban areas using SF6 gas insulated switchgear.

What is the main factor in determining what the grounding resistance will be?

Soil resistivity is the main factor.

How deep does the ground grid need to be buried?

At least 18 inches below grade.

why are substation capacitors banks often utilized?

Since transformers consume reactive power

What is installed with the capacitor bank to facilitate discharging it?

A grounding switch

When are hook stick switches used in a substation?

When voltage application from 15kV to 169kV

What switches operate better in ice conditions?

Double end-break switches

How many degrees rotation does a group operated switch require?

180 degree to open or close

What is corona?

The ionization of the air surrounding energized components, which can produce unacceptably loud crackling or buzzing.

what engineer designs the structural design of the substation?

civil engineer

The simplest and least expensive option for the substation bus is the _____ design.

Radial

When ordering a substation power transformer, no-load and load losses must be taken into consideration. These losses are expressed in?

Watts

The standard which contains the guide for containment and control of oil spills in substations is ___________.

IEEE 980

The simplest and least expensive option for the substation bus is the __________ design.

Radial bus

When ordering a substation power transformer, no load losses must be taken into consideration. These are expressed in _________.

watts

Circuit breakers on distribution voltages typically have a fault interrupting speed of _________ cycles.

3 or 5