The IEC + CEA / CBIP set

A standards set is the group of standards and regulations that a project's design follows. The Standards input selects it for the project, and the IEC + CEA / CBIP set is the default. The set joins the IEC standards with the regulations of the Central Electricity Authority (CEA) of India and the manuals of the Central Board of Irrigation and Power (CBIP). IEEE standards cover the earth mat, the lightning protection and the DC system.

1What a standards set changesCopy link to What a standards set changes

The set is one input that changes most of the design. It sets the voltage levels a project can take and their ratings, clearances and yard sizes. It sets the frequencies, the short-circuit method, the earthing rules and the station's auxiliary supply. It also sets the words, the units and the paper of the deliverables, the device designations on the single-line diagram (SLD), and the compliance checklists. A design step reads these from the project's set, so a change of set marks the steps out of date until the next design run.

In the IEC + CEA / CBIP set the deliverables are in SI units on A1 sheets. The SLD carries the letter codes of IEC 81346-2:2019 with the numbering Indian utilities use (Graphical symbols). The bus scheme per level follows the CEA / CBIP norm, and the SLD names that norm when a project takes another scheme (Bus schemes).

2Standards and regulations per design stepCopy link to Standards and regulations per design step

the table lists the regulations and standards the design follows at each step of the set. A regulation states the requirement, for example that the touch and step voltages are limited to tolerable values. Where a regulation defers to the relevant standards, the standard gives the method and the numbers.

The design's insulation levels follow the CEA table and are checked against the standard insulation levels of IEC 60071-1:2019. The yard's clearances are the level table of the CEA / CBIP practice, checked in the compliance checklist against the minimum clearances of IEC 61936-1:2021.

3Voltage levels and system frequencyCopy link to Voltage levels and system frequency

The set designs pooling substations at 400 kV, 220 kV, 132 kV, 66 kV and 33 kV on the high-voltage (HV) side. A 33 kV HV level is designed as a 33/11 kV substation. The collector (MV) bus is 33 kV, or 11 kV at 66 kV and 132 kV. A level outside its capacity range is still designed, with a warning.

the table lists the switching substations of the set, by the upper and the lower HV level. The 765 kV level is designed as a 765/400 kV switching substation only.

The frequency is 50 Hz, the default, or 60 Hz. The frequency enters the decrement factor of the earth mat's current and the making-current check of the circuit breakers. IEC 62271-100:2008 takes the rated making current as 2.5 times the breaking current at 50 Hz and 2.6 times at 60 Hz (§4.103).

4The CEA regulationsCopy link to The CEA regulations

The CEA regulations are published in the Gazette of India. They state what a substation provides, and in several places they leave the numbers to the relevant standards. The design follows the Central Electricity Authority (Technical Standards for Construction of Electrical Plants and Electric Lines) Regulations, 2022, and the Central Electricity Authority (Measures relating to Safety and Electric Supply) Regulations, 2023.

The construction regulations set the ratings and the arrangement. Reg. 43(1) and Table 6 give the minimum short-time withstand current per level. Reg. 44(2)(a) and Table 7 give the bus scheme per level for an air-insulated (AIS) substation, and Reg. 44(3)(b) and Table 8 for a gas-insulated (GIS) one. Reg. 44(2)(c) asks for shielding against direct lightning strokes by shield wires or masts. Reg. 45(1) and Table 9 give the highest system voltage and the lightning impulse withstand per level.

The safety regulations set the clearances and the protection of people. Reg. 46(2)(i) asks for safety clearances as per the relevant standards. Reg. 46(2)(iii) and Schedule V give the safety working clearance. Reg. 46(2)(vii) asks for separation walls and oil soak pits for apparatus with more than 2000 l of oil. Reg. 50(1)(i) limits the touch and step potential to tolerable values. Reg. 51(ii)(a) asks for an earthed fence of not less than 1.8 m around an outdoor substation.

5The IEC and IEEE standards of the setCopy link to The IEC and IEEE standards of the set

The short-circuit study follows IEC 60909-0:2016. It takes an equivalent voltage source at the fault location with the voltage factor c, and the correction factor of the transformers. The study finds three-phase, phase-to-earth, phase-to-phase and two-phase-to-earth faults at the HV and MV buses. The rating checks compare the currents with the breaking, making and short-time ratings of IEC 62271-100:2008 and IEC 62271-1:2017.

The earth mat follows IEEE Std 80-2013 in both sets. The IEC + CEA / CBIP set checks the tolerable touch and step voltages for a body of 50 kg, and the report also shows the values for 70 kg (Tolerable body current). The mat is of mild steel rod with a corrosion allowance, and its conductor temperature is limited to the design's 500 °C (Conductor sizing). The report adds a cross-check of the grid resistance by the Laurent equation of IS 3043.

The lightning protection of the HV yard follows the rolling sphere of IEEE Std 998-2012, with the striking distance of Mousa from each level's BIL. The MV areas and the building take the LPL I sphere of IEC 62305-3. The DC system follows IEEE 485-2020 for the battery and IEEE 946-2020 for the chargers. The auxiliary supply is 415 V AC with a 220 V DC battery, and a DG set.

6IS 3043 and the CBIP manualsCopy link to IS 3043 and the CBIP manuals

IS 3043:1987, the Indian code of practice for earthing, gives the soil resistivity survey that the design reads. It describes the Wenner method (§36.3.1), the electrode spacings (§36.5.1) and the test in the dry season (§36.1.2). The design takes the soil as uniform when the readings vary within the limit of §36.6.1, and as two-layer otherwise (Soil resistivity and Wenner readings).

The CBIP manuals record Indian utility practice. The design reports the grid resistance against 1 Ω, beside the touch and step check. Its checklist credits that limit to the CBIP Manual on Earthing of AC Power Systems (Publication 311). The typical details of the earth mat follow the practice of the same manual. The device designations on the SLD and the instrument transformer defaults follow the CBIP and POWERGRID practice.

7Compliance checklistsCopy link to Compliance checklists

The set's compliance checklists are CEA / Indian, IEC and IEEE. The CEA / Indian list holds the CEA construction, safety, connectivity and metering regulations, the CBIP manual and IS 3043. The IEC list holds IEC 60071-1, IEC 61936-1, IEC 60909-0, the IEC 62271 switchgear standards, IEC 61869, IEC 60099-4, IEC 60076, IEC 62305-3, IEC 61000-6-5, IEC 61850 and ISO 8528-5. The IEEE list holds IEEE 80, IEEE 998, IEEE 485, IEEE 946 and the IEEE C37 protection guides.

An item states the requirement as a measurable statement and cites its regulation or standard with the clause. An item without a clause cites its standard alone. A clause entered in the Library prints in place of the item's own. Items are numbered per checklist: CEA-01, IEC-01 and IEEE-01 onwards.

An automatic item is checked from the design on each design run, with the design value beside it. Its status is Complies, Does not comply or Needs your review, with the reason for a review. An automatic item that holds by the construction of the design reads Met by design. A manual item takes the user's answer: Complies, Does not comply, Not applicable or Needs your answer, with a note and an evidence reference. An automatic item that needs a review takes the user's answer in the same way. Answers apply without a design run. The checklists download as an XLSX workbook, one sheet per checklist, and as an A4 PDF.