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Selection of System Voltage

The selection of utilization and distribution voltage levels is one of the most important considerations in power system design. System voltages usually affect the economics of equipment selection and plant expansion more than any other single factor. It behooves the power system engineer to consider carefully the problem when designing the distribution system.

Voltage Classes

The various voltage...

Low-voltage Circuit Breaker Distribution Systems

High Capacity Service Entrance

High capacity service entrances are those installations having continuous current ratings above 600 amperes and available fault currents up to 130kA rms symmetrical amperes at 240 volts and 85kA at 460 volts. The continuous-current requirements for this service entrance are usually beyond the capacity of molded-case circuit breakers, hence metal-enclosed switchgear with its higher capacity circuit...

Why Wye-Wye Transformer Connection is Bad?

Transformer Primary Connections

Transformer primaries are usually connected in delta. The wye connection is occasionally used and may or may not have its neutral grounded. If the transformer secondary is connected wye, as in a four-wire 415Y/240-volt system, the best connection for the primary is delta. Unbalanced loads do not create abnormal regulation problems. Third-harmonic magnetizing currents are contained within...

System Grounding

Secondary Grounding

When a wye connected circuit and solidly or effectively grounded neutral is used, the following benefits are obtained in addition to the dual voltage capability, (a) A single line-to-ground fault will cause sufficient ground current to flow to actuate standard protective relays and thereby isolate the faulted circuit, and identify the source of trouble, (b) The maximum voltage to ground...

Comparison of Common Induction Motor Starting Methods

Motor Starting Phenomenon

The three-phase induction motors represent the most significant load in the industrial plants, over the half of the delivered electrical energy. Motor loads specially the medium and large size ones, require high amount of reactive power for a short period during their startup. The high reactive power drawn from the system causes voltage dips at startup time...
Learn the basics

Tutorials

MVA Method

At this times where supercomputers could fit into a mobile phone and utility softwares are always available to do particular tasks, most Electrical Engineers tend to forget how to implement …

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Short Circuit Study
What is a Short Circuit Study? A short circuit study calculates the short circuit capacity at designated locations within a...
MVA Method Short Circuit Calculation
A Short Circuit Study is an important tool in determining the ratings of electrical equipment to be installed...
MVA Method Load Flow Calculation
In previous tutorials for the MVA method, we have discussed the importance of Short Circuit Study, combining KVAs and...
MVA Method for 3-Winding Transformer
In previous tutorials, the examples provided were mostly for 2-winding transformers. In this tutorial, fault calculations for a 3-winding...
Complex MVA Method – Part 3
In Part 2, we have seen how to combine MVAs connected...
Complex MVA Method
The normal MVA method, despite its simplicity, provides only an approximate solution to determine the fault levels in a...
Complex MVA Method – Part 2
After presenting the equations that we will be using for the Complex MVA Method in Complex MVA Method – Part 4
In Part 1, Part 2, and Part...
Combining KVAs
KVAs in series. The total KVAs in series (KVAtotal) is the reciprocal sum or inverse sum of all series...

Cable Selection

Cable Selection – Single Phase Earth Conductor Sizes Fault Loop Impedance High Voltage Cable Selection – Underground Cables Selection for Motors

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Cable Selection – Single Phase
Note: This will be the first of a series of tutorials for the selection of cables. The objective of this...
Fault Loop Impedance
Note: This is the second part of a series of tutorials for cable selection. We have done cable selection based...
Cables Selection for Motors
When selecting a suitable cable size for a motor, there are more parameters to consider than when selecting cables...
High Voltage Underground Cable Selection
Unlike the other Cable Selection tutorials which deals with low voltage (LV) cables,...
Earthing Conductor Sizes
The following table lists the recommended minimum sizes of earthing conductors. Note: This serves only as a guide, calculations are...
Arc Flash Hazards
It's not too long ago that arc flash hazards has become an important part of electrical design. More clients...
IEEE 1584 Arc Flash Calculations
IEEE 1584 provides empirical formulas for determining arcing fault current, flash protection boundaries, and incident energy. The formulas are...
Time-Current Curves Using Excel – Part 1
In these articles, I have discussed the methodology on how to create time-current curves using excel.
  1. Creating Coordination Curves...
Time-Current Curves
Discrimination & coordination using Time-Current Curves
  1. TC Curves Part 1 - Introduction
  2. Time-Current Curve Part 2 – Discrimination
    In Part 1, I have discussed the basics of using excel in plotting time-current curves. In...
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