Other Power Quality Solutions

Load Shedding Analysis

Load shedding is a special form of dynamic study most frequently associated with electrical systems having in-plant generation. The time period of examination is usually longer due to the slower response of governors. Loss of a major source, usually the utility, can have a severe effect on plant voltage and frequency. Rapid corrective action may be required.

A SPGS load-shedding study can help determine if standard load-shedding relays are adequate or if a computer-based load-shedding system is required. SPGS engineers examine different operating scenarios to determine the speed and amount of load to be shed for successful recovery, while keeping critical loads through a disturbance.

Motor Starting Analysis

SPGS' motor starting analysis identifies the expected voltage dip and acceleration time for a motor and the effects of motor starting on a system. Alternate starting methods, such as across-the-line, reactor, capacitor, or auto-transformer start, can be explored.

If system voltage dips are a concern, SPGS engineers will propose the appropriate solutions. For calculating acceleration times, they will employ advanced, dynamic simulation with inertia and other machine data.

Relay Coordination

Proper application and coordination of over-current relays and other protective devices is vital in a system requiring reliable electrical service. SPGS engineers bring the critical experience needed for the proper application of ANSI and NEC requirements to equipment protection.

In addition to relays that respond to short circuits, low-voltage breakers, differential, directional, power, under-voltage, out-of-step, and other special protective relays often need to be set. This SPGS study will include detailed tables listing the recommended settings and discussion of any limitations.

Short-Circuit Analysis

Short-circuit calculations are required to correctly apply equipment in accordance with NEC, and ANSI standards. Depending on the size and utility connection, the amount of detail required to perform these calculations can vary greatly. SPGS’ short-circuit analysis will include calculations performed in accordance with the latest ANSI standards.

Switches, fuses, and breakers that need to interrupt or close into a fault are of special concern. Cables and bus-work also have short-circuit withstand limitations, and a thorough study will examine non-interrupting equipment, as well as switches and breakers. Standards such as ANSI C37.010 and C37.13 outline the recognized calculation methods for these equipment-rating analyses.

Short-circuit calculations are required for the application and coordination of protective relays and the rating of equipment. All fault types can be simulated. SPGS’ short-circuit study provides a detailed report identifying breaker ratings, breaker fault duties, discussions, and recommendations for any deficiencies found.

System Stability Analysis

The stability of synchronous motors and generators has long been a design consideration in industrial and co-generation plants, as well as utility systems. It is necessary to ensure the network, synchronous machines, and protective systems will function adequately so faults do not interrupt operation.

Where instability is shown to be a potential problem, several practical alternatives can usually be used to eliminate the source of the problem. In some situations, changes to the network can improve stability; while in others, protective systems can be installed to avoid machine damage and minimize the disturbance.

A SPGS system stability study can include:

• Induction generator over-excitation from capacitors
• Induction motor low- and high-voltage effects
• Motor transfer analysis when switching sources
• Re-accelerating analysis to guide plant operators
• Impact loading on motor shafts
• Emergency generator performance applied to load recovery
• General system stability

One form of output from a dynamic study is graphical time response or impedance plots.

These plots can show variations in voltage, machine angle, frequency, line flows, and apparent impedance.