Protective_Devices_Coordination_Study_TechSpecs_JULY_2012.pdf

PROTECTIVE DEVICES COORDINATION STUDY

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JULY 2012 (100% FINAL)

Protective Devices Coordination Study Technical Specs

This document contains proprietary information and is protected by Copyright laws and should hence not be copied or published, in part or in whole, in any form or manner without the written approval of the Integrated Bureau for Engineering & Consultations (IBEC). The document shall be used for viewing and

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JULY 2012 (100% FINAL)

MINIMUM REQUIREMENTS FOR A

PROTECTIVE DEVICE COORDINATION STUDY

Power systems must be able to safely deliver power to electrical loads during normal operation and the system must also be able to survive and protect both personnel and equipment during abnormal/faulted conditions. A Short Circuit and Coordination Study, or a Power System Study, is performed to determine if the power system is properly rated for normal operation and abnormal (fault) conditions.

Before conducting a Protective Device Coordination (PDC) study, a Short Circuit study must be available. This study calculates the available fault currents at all busses throughout the electrical distribution system. After the short circuit study is available, the PDC study evaluates the set points/ratings of protective devices and ensures that the device closest to a fault opens to remove power to the fault while maintaining power to as much electrical equipment as possible.

PDC STUDY REQUIREMENTS

Data Collection:

The data necessary for the Short Circuit study should have been collected from power system drawings and field verification. As much field verification as possible is crucial to ensure an accurate study since drawings are often not updated. Special emphasis should be placed on getting data about cable runs (size, configuration, and length), fuse types and sizes, starter/breaker ratings, motor ratings, and transformer %Z values and ratings. Make sure the utility contribution is obtained or verified with the local utility and that it has been included in the short circuit calculation.

For the PDC study, field verify the set points of every MV relay and LV breaker. Ensure that the correct manufacturer is determined and that model numbers for trip units, relays or other protective devices (data which identifies the trip characteristic of the protective device) is available and verified or is collected from the field. Field verification of the set points/fuse sizes should be done for all main distribution switchgear down to the Power Distribution Panels and MCC level and up to the Sub-distribution panels level.

The short circuit study should calculate both the available 3 phase fault current and the single phase to ground available fault current.

Software Requirements:

The PDC Study should be conducted using Professional grade, world renowned software. The software should contain a library of and be able to output in graphic format the Time Current Characteristics (TCC) of the different protective devices. The software should be able to reflect protective device settings on the TCC. The device libraries of the software should have been verified to match characteristics available in manufacturer catalogs.

This document contains proprietary information and is protected by Copyright laws and should hence not be copied or published, in part or in whole, in any form or manner without the written approval of the Integrated Bureau for Engineering & Consultations (IBEC). The document shall be used for viewing and

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PDC Study Bases:

The complete study should be conducted using Time Current Characteristics (TCCs). No Discrimination by tables is accepted.

The complete study should be conducted using Time Discrimination and Current Discrimination. No Discrimination by Energy is accepted except as an approximate secondary evaluation of the circuit coordination, when all measures using TCCs and applying Time and Current Discrimination concepts prove insufficient.

Current selectivity up to the downstream 3-phase short circuit level should be sufficient to assume “Total” selectivity of the stream (circuit).

The protective device tripping, via the regular over current protections, on single line to ground (SLG) short circuit (earth fault) must be checked and verified for TN-C or TN-S systems. For TT systems the TCCs should show the Ground Fault Protection Characteristics and which should be revised to guarantee tripping on the downstream SLG fault level.

Input Data Section:

The PDC study should include in tabular format all the protective device data and settings that was collected or verified and which will be used as input data to the study. This is essential to confirm what values were used in the study.

As Found Settings TCCs:

All protective devices in the study must be shown on at least one TCC. TCCs must reference a small schematic diagram (single line diagram) showing the devices on the TCC. Do not put too many devices on one TCC. It tends to make the TCCs difficult to read. All TCCs must have a name, number, or title to differentiate the curves. All TCCs must state their reference voltage and current scale.

New Settings TCCs:

A new TCC must be made to show recommended settings of each device whose set points or size is changed by the person performing the PDC study. The new settings made to a particular device in one TCC (for example the incoming of the main distribution board) must be reflected to the settings of the same device in other TCCs that show the same device.

Study Recommendations:

A list of recommendations must be given stating changes the vendor performing the study believes will improve the overall electrical system design and/or coordination. Things recommended to be changed can be as simple as increasing a fuse size to changing breaker setpoints to pulling additional cables. Each recommendation must state which As Found Setting TCC and New Setting TCC the recommendation refers to.

This document contains proprietary information and is protected by Copyright laws and should hence not be copied or published, in part or in whole, in any form or manner without the written approval of the Integrated Bureau for Engineering & Consultations (IBEC). The document shall be used for viewing and

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Set Point Tables:

A table stating the as found sensor, plug, and set points of each breaker or protective device is required.

In the same table, the recommended (new) sensor, plug, and setpoints for each device must also be shown.

Additional Requirements:

The following data should also be included on the TCCS and the recommendations should include suggestions to remedy any problems that may be discovered while reviewing this data on the TCC and in relation to the respective protective devices:

• Transformer Damage Curves (standard curves are acceptable).

• Transformer Inrush Current (standard values will be accepted if manufacturer specific values are not available).

• Cable Damage Curves (standard curves are acceptable).

• 3-phase fault level at all buses included in the TCC.

• Single line to ground fault level at all buses included in the TCC.

• Single line diagram showing all protective devices and buses included in the TCC.

• Device Names, Types, Models, and settings.

• Cable Names and cross-section.