Many industrial systems depend on the operation of protective relay for the protection against excess current involving phase and earth faults. The main role of a protection system is to ensure that only the faulty section is isolated so as to minimize the interruption of supply to other sections of the network. Coordinating various types of protective relay in a network can be very tedious and time consuming. Even for a very simple radial network, the assessment of relay grading and the presentation of several relay curves can also be time consuming. The visually interactive package VipCag is developed to provide a comprehensive computer-aided tool to assess and automate the grading of overcurrent and earth fault protection in a distribution network.

1.          Distribution Network Representation

 Five different voltages from 400 V, 6.6 kV, 11 kV, 22 kV, 33 kV and 66 kV can be simultaneously represented. The user may also change any one of the five default voltages to cater for the operation of different networks. Currently, VipCag can handle up to 100 nodes, 100 lines, 20 generators, 20 transformers and 20 motors.

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2.         Modeling of Protective Devices

Practically all types of protective devices including IDMT relay, definite-time-lag (DTL) relay, fuse, direct-acting LV circuit breakers and electronic trip units are modeled.. For IDMT relay, the user may select standard 3/10, very inverse, extremely inverse or 1.3/10 relay. For fuses, the whole range of BS88 LV fuse and some HT fuses are included. For direct-acting LV circuit breakers, four typical types of thermal-electromagnetic tripping curves are provided. Different types of electronic trip units such as STR28D, STR38S, etc can also be included. In addition, the time-current characteristic of a transformer inrush current and that of motor starting by using different types of starters can also be modeled.

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3.         Interactive Tools for Network Editing

Visually interactive tools are provided for the user to create or edit a graphical distribution network and to specify parameters such as load and fault currents at each substation, circuit rating, CT ratio and types of relays for each feeder, transformer or and generator. Tools are also provided for the user to insert, delete or move a busbar/feeder on the single line diagram. The user may right-click a network element to view or change the technical specification of a line, a bus or a transformer.

Alternatively, under the input menu, the user may view or edit data from a list of tabulated data such as load in MW, MVAr, short circuit current and earth fault current in kA under the load/fault sub-menu. The user may also change the type of cable, cable rating, sending end and receiving end CT ratio under the cable sub-menu. Under the graph menu, the user may view the time-current characteristics of the relay curve at a particular setting, or a number of relay curves of different types of relay at some specific settings. The user may adjust one or a number of settings and check the coordination graphically on the log-log scale.

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4.         Built-in Auto Grading Algorithm

By considering the possible CT and relay errors, circuit breaker operating time and a safety margin, the minimum grading marginbetween each protective zone is determined. The auto grading allows the user to select grading for earth fault relays or for overcurrent relays. In the auto grading process, the user may select the option of either bottom up grading (i.e. grading starting from the most downstream zone and grade upwards) or top down grading (i.e. grading starting from a given upstream settings such as those settings specified by the utility at the intake substation and grade downwards). Depends on whether digital type or electromagnetic type of relays, the available plug setting will be adjusted accordingly. In addition, the user may also specify the required percentage of overload separately for feeder and transformer.

For earth fault auto grading, the user may specify the required plug setting, the minimum TMS of either 0.05 or 0.1 and the starting TMS for bottom up grading. For delta-earthed-wye transformer, the recommended earth fault settings at the wye-terminal will be checked to ensure that the operating time of the overcurrent relay at the delta terminal will not operate prior to the operation of the earth fault relay at the wye terminal.

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5.        Tabulated Presentation

 The recommended relay settings of the whole network will be presented in one table for overcurrent settings and another table for earth fault settings. For each table a summary of grading specification such as grading method, minimum grading margin and the grading assumptions and requirements will be listed on the top of the table followed by a circuit by circuit listing.  For each circuit, the circuit ID, type of relay, CT ratio, recommended plug and time multiplier settings, high set current, fault current, relay operating time, upstream operating time and the actual margin in seconds between each relay and its upstream relay are tabulated for the whole network.

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6.        Graphical Presentation

The user may also click one or a number of circuits from the tabulated presentation and a graphical presentation of the relay curves and operating times at the specified fault current will be plotted. The graphical display is shown on a log-log scale with time in seconds in the x-axis and fault current in amperes expressed at a specified voltage in the y-axis. The current in the Y-axis can be re-specified as a current in another voltage level and the relay curves and operating time will be adjusted accordingly. The relay operating times for a given fault current are superimposed on the respective relay curves and the time margin in seconds between each feeder can be clearly observed. Other time current characteristic curves such as motor starting, transformer inrush current, transformer withstand curve, fuse and LV breaker’s thermal-electromagnetic tripping curve can all be shown in the same diagram. Visually interactive tools are also provided for the user to re-specify/adjust the overcurrent or earth fault settings for any feeder or transformer. The current setting of each relay curve can be adjusted by simply clicking the appropriate button expressed in ampere or in percentage plug setting. The TMS setting can also be specified in an analog sliding scale or simply key-in a digital value from 0.05 to 1.0.

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7.     LICENSE AND FEE

VipCag is available under a license for a single-copy price of Singapore dollars S$6,800.00. Support and updates are provided free of charge for 12 months.

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8.      HOW TO ORDER

Send purchase order by e-mail to cyteo@ntu.edu.sg, or by telephone call to Byte Power Publications at (65) 6256 0101   and arrangement will be made for site demo/installation. 

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9.     TYPICAL DISPLAY

* Click on the thumbnails below for sample display

    Creating a typical single-line diagram for Stimulation

    Recommended Overcurrent Settings

    Overcurrent Settings for the 10 MVA transformer

    Overcurrent Settings for FMC1A and starting of the Water Chiller Motor

    Overcurrent Settings of the 3 MVA transformer

    Motor Starting and Overcurrent Settings for the Glycol Chiller

    Recommended Earth Fault Settings

    Earth Fault Settings of FMC1A and the 10 MVA transformer at 6.6 kV

    Earth Fault Settings of the 3MVA transformer and FS2A at 6.6 kV

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10H, Braddell Hill, #23-30

Singapore 579727

Tel:  (65) 6256-0101