Auxiliary Transformer Sizing (Substation Primary Design Course)

In this post, we wil explain auxiliary transformer sizing, as per SEC/National Grid standards. Auxiliary transformers play a critical but often underestimated role in substation design. While power transformers transmit energy to the grid, auxiliary transformers ensure the substation itself stays alive—supplying power to protection, control, HVAC, lighting, motors, communication systems, and essential services.This is our 5th post that is part of Extra High Voltage EHV Substation Design & 380kV Substation Design. If you are new on our website it is recommended to read first the below Posts

• 380kV Gantries & Gantry Equipment
• Inside a 380kV BSP: Overall Layout Drawing Explained
• 380kV Gas-Insulated Switchgear (GIS)
• Power Transformers

1. Why Auxiliary Transformer Sizing Matters

Most project technical specifications mention a minimum auxiliary transformer rating, but accepting these values without verification represents a significant engineering risk. During the design stage, detailed calculations must substantiate or challenge these preliminary figures. This verification process isn’t merely bureaucratic—it’s fundamental to ensuring decades of reliable substation operation.

• That value is often generic
• It may not reflect actual connected loads
• It may ignore future expansion
• It may violate loading limits defined by standards

👉 Design engineers are responsible for verification, not blind acceptance.

Improper sizing can lead to:

• Overloading and premature failure
• Nuisance tripping
• Inability to support future bays or equipment
• Safety and reliability risks

2. Key Factors for SST Sizing

To size an auxiliary transformer, engineers must consider:

2.1 Ultimate Substation Configuration:

Account for current and future load requirements (e.g., planned expansions).Transformer sizing must account for both current requirements and future load growth. Substations often expand over their 30-40 year operational lifespan, and auxiliary systems must accommodate this evolution without requiring premature transformer replacement.

Design Philosophy: Size for the 20-year horizon, not just today’s needs. This forward-looking approach represents the most cost-effective lifecycle strategy

2.2 80% Loading Limit:

As per the SEC standard TES-P-119.35, clause 3.1.2 it is required that simultaneous peak loading on the auxiliary transformer excluding the power transformer oil filtration socket load shall not exceed 80% of the station service transformer capacity. This 20% margin serves multiple purposes:

• Improves efficiency by operating in the optimal region of the load curve
• Accommodates unexpected load spikes
• Reduces thermal stress, extending transformer life
• Provides capacity for unanticipated future loads

2.3 Diversity Factor:

A multiplier to reflect realistic load demand (e.g., not all loads operate at full capacity simultaneously). Diversity factors recognize that not all connected loads operate simultaneously at their maximum capacity. To understand diversity factor we must understand continuous and momentary loads,

Continuous vs. Momentary Loads

Continuous Loads:

• HVAC systems (when maintaining 25°C room temperature)
• 125V DC battery chargers
• Protection and control panels
• Communication equipment
• Cubic lighting

Momentary/Intermittent Loads:

• Sump pump motors
• Transformer WTTC (Wait Tap Changer) motors
• Circuit breaker operating motors
• Oil filtration systems (specifically excluded from continuous calculations per TSP 119.35 Clause 3.1.4)

Diversity Factor Application Guidelines

1. Lighting Loads: Diversity factor = 1.0 (all considered fully loaded)
2. Receptacles: 50% loading assumption for indoor/outdoor receptacles
3. Panel Heaters: Excluded if full HVAC load included (maintains 25°C)
4. Duct Heaters: Excluded when HVAC load fully accounted
5. Receptacle Groups: One receptacle per group assumed continuously loaded

2.4 Standards Compliance:

Adherence to

• Project Specification PTS-XXXXXXX- Project Technical Specification
• SEC Standard: TES-P-119.35.Rev-0 – Station Auxiliary Transformer Sizing
• SEC Standard: TES-P-119.30.Rev-2 – Auxiliary AC/DC Panels

Step-by-Step Sizing Methodology

Phase 1: Data Collection and Documentation

1. Comprehensive Load Inventory: Obtain complete AC load listing from project client, including all future planned loads
2. Standards Review: Thoroughly study applicable standards for load categorization requirements
3. Equipment Specifications: Gather detailed specifications for all substation equipment with AC loads

Phase 2: Tabular Load Analysis

The systematic approach utilizes a detailed table structure (as exemplified in Table 1 for a 13.8kV/400-230V auxiliary transformer):

Equipment	Rated KVA	Quantity	Total Rated KVA	Diversity Factor	Operating KVA
125V Battery Charger	50	2	100	0.5	50
Lighting Panels	60.129	1	60.129	1.0	60.129
HVAC System	75	1	75	1.0	75
…	…	…	…	…	…

Phase 3: Calculation and Selection

Example Calculation:

1. Sum Operating KVA: Total all operating KVA values from table
   • Example: 358 KVA (sum of diversified loads)
2. Apply 80% Loading Rule:$$\text{Required Rating}=\frac{\text{Total Operating KVA}}{0.8}=\frac{358}{0.8}=448\text{ KVA}$$Required Rating=0.8Total Operating KVA​=0.8358​=448 KVA
3. Select Standard Rating: Choose next available market standard size
   • 448 KVA → Select 500 KVA transformer

It is strongly recommended that you have the Idea about Number of AC & DC Panels required inside a BSP. Panels Required in Substations

Typical Loads of a 380/132kV BSP MAIN DB BUS-1

Feeder No.	Description	Voltage	Load in kW (a)	Quantity (b)	Connected Load (c) = (a)x(b)	Diversity Factor (d)	Operated Load (e) = (c)x(d)
1.1	300A, OIL FILTERATION SOCKET (SGT-1)	400	147.22	1	147.22	0.00	0.0
1.2	300A, OIL FILTERATION SOCKET (SGT-2)	400	147.22	1	147.22	0.00	0.0
1.3	300A, OIL FILTERATION SOCKET (SGT-3)	400	147.22	1	147.22	0.00	0.0
1.4	300A, OIL FILTERATION SOCKET (BUS REACTOR)	400	147.22	1	147.22	0.00	0.0
1.5	300A, OIL FILTERATION SOCKET (LINE REACTOR)	400	147.22	1	147.22	0.00	0.0
1.6	300A, OIL FILTERATION SOCKET (LINE REACTOR)	400	147.22	1	147.22	0.00	0.0
1.7	300A, OIL FILTERATION SOCKET (LINE REACTOR-FUTURE)	400	147.22	1	147.22	0.00	0.0
1.8	300A, OIL FILTERATION SOCKET (LINE REACTOR-FUTURE)	400	147.22	1	147.22	0.00	0.0
1.9	300A, OIL FILTERATION SOCKET (T-301)	400	147.22	1	147.22	0.00	0.0
1.10	SDB-1 (CONTROL BUILDING) SUPPLY-1	400	29.31	1	29.31	0.50	14.7
1.11	SDB-2 (380kV GIS BUILDING) SUPPLY-1	400	88.03	1	88.03	0.50	44.0
1.12	SDB-3 (132kV GIS-1 BUILDING) SUPPLY-1	400	3.23	1	3.23	0.50	1.6
1.13	SDB-4 (132kV GIS-2 BUILDING) SUPPLY-1	400	3.23	1	3.23	0.50	1.6
1.14	SDB-5 COMMUNICATION DB (COMMUNICATION ROOM) SUPPLY-1	400	5.00	1	5.00	0.50	2.5
1.15	SDB-6 (CUSTOMER ROOM) SUPPLY-1	400	22.78	1	22.78	0.50	11.4
1.16	SDB-7 COMMUNICATION DB (CUSTOMER ROOM) SUPPLY-1	400	4.00	1	4.00	0.50	2.0
1.17	SDB-8 (PUMP ROOM) SUPPLY-1	400	5.86	1	5.86	0.50	2.9
1.18	SDB-9 (SECURITY BUILDING) SUPPLY-1	400	53.60	1	53.60	0.50	26.8
1.19	ILP-1 (CONTROL BUILDING) SUPPLY-1	400	22.96	1	22.96	0.50	11.5
1.20	ILP-2 (380kV GIS BUILDING) SUPPLY-1	400	16.95	1	16.95	0.50	8.5
1.21	ILP-3 (132kV GIS-1 BUILDING) SUPPLY-1	400	11.41	1	11.41	0.50	5.7
1.22	ILP-4 (132kV GIS-2 BUILDING) SUPPLY-1	400	11.41	1	11.41	0.50	5.7
1.23	ILP-5 (CUSTOMER ROOM) SUPPLY-1	400	3.37	1	3.37	0.50	1.7
1.24	OLP-1 (CONTROL BUILDING) SUPPLY-1	400	40.14	1	40.14	0.50	20.1
1.25	OLP-2 (380kV GIS BUILDING) SUPPLY-1	400	50.88	1	50.88	0.50	25.4
1.26	HVAC POWER PANEL-1 (380kV GIS BUILDING) SUPPLY-1	400	87.10	1	87.10	0.50	43.6
1.27	HVAC POWER PANEL-2 (380kV GIS BUILDING) SUPPLY-1	400	87.10	1	87.10	0.50	43.6
1.28	HVAC POWER PANEL-3 (380kV GIS BUILDING) SUPPLY-1	400	87.10	1	87.10	0.50	43.6
1.29	HVAC POWER PANEL-4 (132kV GIS-1 BUILDING) SUPPLY-1	400	70.40	1	70.40	0.50	35.2
1.30	HVAC POWER PANEL-5 (132kV GIS-1 BUILDING) SUPPLY-1	400	70.40	1	70.40	0.50	35.2
1.31	HVAC POWER PANEL-6 (132kV GIS-2 BUILDING) SUPPLY-1	400	70.40	1	70.40	0.50	35.2
1.32	HVAC POWER PANEL-7 (132kV GIS-2 BUILDING) SUPPLY-1	400	70.40	1	70.40	0.50	35.2
1.33	HVAC POWER PANEL-8 (CONTROL BUILDING) SUPPLY-1	400	70.40	1	70.40	0.50	35.2
1.34	HVAC POWER PANEL-9 (CONTROL BUILDING) SUPPLY-1	400	150.00	1	150.00	0.50	75.0
1.35	HVAC POWER PANEL-10 (CUSTOMER ROOM) SUPPLY-1	400	30.00	1	30.00	0.50	15.0
1.36	HVAC CONTROL PANEL-1 (380kV GIS BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.37	HVAC CONTROL PANEL-2 (380kV GIS BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.38	HVAC CONTROL PANEL-3 (380kV GIS BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.39	HVAC CONTROL PANEL-4 (132kV GIS-1 BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.40	HVAC CONTROL PANEL-5 (132kV GIS-1 BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.41	HVAC CONTROL PANEL-6 (132kV GIS-2 BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.42	HVAC CONTROL PANEL-7 (132kV GIS-2 BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.43	HVAC CONTROL PANEL-8 (CONTROL BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.44	HVAC CONTROL PANEL-9 (CONTROL BUILDING) SUPPLY-1	400	15.00	1	15.00	0.05	0.8
1.45	HVAC CONTROL PANEL-10 (CUSTOMER ROOM) SUPPLY-1	400	10.00	1	10.00	0.05	0.5
1.46	125V DC BATTERY CHARGER-1 (380kV GIS SYSTEM)	400	106.25	1	106.25	0.50	53.1
1.47	125V DC BATTERY CHARGER-3 (132kV GIS SYSTEM)	400	87.50	1	87.50	0.50	43.8
1.48	48V DC BATTERY CHARGER-1 (COMMUNICATION ROOM)	400	33.60	1	33.60	0.50	16.8
1.49	COOLING FAN SUPPLY – SGT-1 SUPPLY-1	400	46.35	1	46.35	0.50	23.2
1.50	COOLING FAN SUPPLY – SGT-2 SUPPLY-1	400	46.35	1	46.35	0.50	23.2
1.51	COOLING FAN SUPPLY – SGT-3 SUPPLY-1	400	46.35	1	46.35	0.50	23.2
1.52	COOLING FAN SUPPLY – SGT-4 SUPPLY-1	400	46.35	1	46.35	0.50	23.2
1.53	COOLING FAN SUPPLY – SGT-5 SUPPLY-1	400	46.35	1	46.35	0.50	23.2
1.54	COOLING FAN SUPPLY – SGT-6 SUPPLY-1	400	46.35	1	46.35	0.50	23.2
1.55	63A, GAS FILLING RECEPTACLE (380kV GIS)	400	30.92	1	30.92	0.00	0.0
1.56	63A, GAS FILLING RECEPTACLE (380kV GIS)	400	30.92	1	30.92	0.00	0.0
1.57	63A, GAS FILLING RECEPTACLE (380kV GIS)	400	30.92	1	30.92	0.00	0.0
1.58	63A, GAS FILLING RECEPTACLE (380kV GIS) (FUT.)	400	30.92	1	30.92	0.00	0.0
1.59	63A, GAS FILLING RECEPTACLE (132kV GIS-1)	400	30.92	1	30.92	0.00	0.0
1.60	63A, GAS FILLING RECEPTACLE (132kV GIS-1)	400	30.92	1	30.92	0.00	0.0
1.61	63A, GAS FILLING RECEPTACLE (132kV GIS-1)	400	30.92	1	30.92	0.00	0.0
1.62	63A, GAS FILLING RECEPTACLE (132kV GIS-2)	400	30.92	1	30.92	0.00	0.0
1.63	63A, GAS FILLING RECEPTACLE (132kV GIS-2)	400	30.92	1	30.92	0.00	0.0
1.64	63A, GAS FILLING RECEPTACLE (132kV GIS-2)	400	30.92	1	30.92	0.00	0.0
1.65	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
1.66	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
1.67	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
1.68	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
1.69	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
1.70	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
1.71	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 380kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
1.72	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 380kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
1.73	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 132kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
1.74	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 132kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
1.75	63A, WELDING RECEPTACLE FOR POWER TRANSFORMER SGT-1	400	30.92	1	30.92	0.00	0.0
1.76	63A, WELDING RECEPTACLE FOR POWER TRANSFORMER SGT-2	400	30.92	1	30.92	0.00	0.0
1.77	63A, WELDING RECEPTACLE FOR POWER TRANSFORMER SGT-3	400	30.92	1	30.92	0.00	0.0
1.78	63A, WELDING RECEPTACLE FOR REACTORS	400	30.92	1	30.92	0.00	0.0
1.79	63A, WELDING RECEPTACLE FOR SST-1	400	30.92	1	30.92	0.00	0.0
1.80	63A, WELDING RECEPTACLE FOR PACU 1A (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
1.81	63A, WELDING RECEPTACLE FOR PACU 2A (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
1.82	63A, WELDING RECEPTACLE FOR PACU 3A (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
1.83	63A, WELDING RECEPTACLE FOR PACU 4A (132kV GIS-1 BUILDING)	400	30.92	1	30.92	0.00	0.0
1.84	63A, WELDING RECEPTACLE FOR PACU 5A (132kV GIS-1 BUILDING)	400	30.92	1	30.92	0.00	0.0
1.85	63A, WELDING RECEPTACLE FOR PACU 6A (132kV GIS-2 BUILDING)	400	30.92	1	30.92	0.00	0.0
1.86	63A, WELDING RECEPTACLE FOR PACU 7A (132kV GIS-2 BUILDING)	400	30.92	1	30.92	0.00	0.0
1.87	63A, WELDING RECEPTACLE FOR PACU 8A (CONTROL BUILDING)	400	30.92	1	30.92	0.00	0.0
1.88	63A, WELDING RECEPTACLE FOR PACU 9A (CONTROL BUILDING)	400	30.92	1	30.92	0.00	0.0
1.89	63A, WELDING RECEPTACLE FOR PACU 10A (CUSTOMER ROOM)	400	30.92	1	30.92	0.00	0.0
1.90	HV TEST SOCKET (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
1.91	HV TEST SOCKET (132kV GIS-1 BUILDING)	400	30.92	1	30.92	0.00	0.0
1.92	PORTABLE CHARGER-1 (125V DC BATTERY CHARGER-1)	400	29.42	1	29.42	0.00	0.0
1.93	PORTABLE CHARGER-3 (125V DC BATTERY CHARGER-3)	400	29.42	1	29.42	0.00	0.0
1.94	SDB-10 (EXTERNAL TELECOM SHELTER) SUPPLY-1	400	8.00	1	8.00	0.50	4.0
1.95	VENTILATION CONTROL PANEL (380kV GIS BUILDING) SUPPLY-1	400	25.00	1	25.00	0.05	1.3
1.96	VENTILATION CONTROL PANEL (132kV GIS-1 BUILDING) SUPPLY-1	400	50.00	1	50.00	0.05	2.5
1.97	VENTILATION CONTROL PANEL (132kV GIS-2 BUILDING) SUPPLY-1	400	50.00	1	50.00	0.05	2.5
1.98	VENTILATION CONTROL PANEL (CONTROL BUILDING) SUPPLY-1	400	50.00	1	50.00	0.05	2.5

Typical Loads of a 380/132kV BSP MAIN DB BUS-2

Feeder No.	Description	Voltage	Load in kW (a)	Quantity (b)	Connected Load (c) = (a)x(b)	Diversity Factor (d)	Operated Load (e) = (c)x(d)
2.1	300A, OIL FILTERATION SOCKET (SGT-4)	400	147.22	1	147.22	0.00	0.0
2.2	300A, OIL FILTERATION SOCKET (SGT-5)	400	147.22	1	147.22	0.00	0.0
2.3	300A, OIL FILTERATION SOCKET (SGT-6)	400	147.22	1	147.22	0.00	0.0
2.4	300A, OIL FILTERATION SOCKET (BUS REACTOR)	400	147.22	1	147.22	0.00	0.0
2.5	300A, OIL FILTERATION SOCKET (LINE REACTOR)	400	147.22	1	147.22	0.00	0.0
2.6	300A, OIL FILTERATION SOCKET (LINE REACTOR)	400	147.22	1	147.22	0.00	0.0
2.7	300A, OIL FILTERATION SOCKET (LINE REACTOR-FUTURE)	400	147.22	1	147.22	0.00	0.0
2.8	300A, OIL FILTERATION SOCKET (LINE REACTOR-FUTURE)	400	147.22	1	147.22	0.00	0.0
2.9	300A, OIL FILTERATION SOCKET (T-302)	400	147.22	1	147.22	0.00	0.0
2.10	SDB-1 (CONTROL BUILDING) SUPPLY-2	400	29.31	1	29.31	0.50	14.7
2.11	SDB-2 (380kV GIS BUILDING) SUPPLY-2	400	88.03	1	88.03	0.50	44.0
2.12	SDB-3 (132kV GIS-1 BUILDING) SUPPLY-2	400	3.23	1	3.23	0.50	1.6
2.13	SDB-4 (132kV GIS-2 BUILDING) SUPPLY-2	400	3.23	1	3.23	0.50	1.6
2.14	SDB-5 COMMUNICATION DB (COMMUNICATION ROOM) SUPPLY-2	400	5.00	1	5.00	0.50	2.5
2.15	SDB-6 (CUSTOMER ROOM) SUPPLY-2	400	22.78	1	22.78	0.50	11.4
2.16	SDB-7 COMMUNICATION DB (CUSTOMER ROOM) SUPPLY-2	400	4.00	1	4.00	0.50	2.0
2.17	SDB-8 (PUMP ROOM) SUPPLY-2	400	5.86	1	5.86	0.50	2.9
2.18	SDB-9 (SECURITY BUILDING) SUPPLY-2	400	53.60	1	53.60	0.50	26.8
2.19	ILP-1 (CONTROL BUILDING) SUPPLY-2	400	22.96	1	22.96	0.50	11.5
2.20	ILP-2 (380kV GIS BUILDING) SUPPLY-2	400	16.95	1	16.95	0.50	8.5
2.21	ILP-3 (132kV GIS-1 BUILDING) SUPPLY-2	400	11.41	1	11.41	0.50	5.7
2.22	ILP-4 (132kV GIS-2 BUILDING) SUPPLY-2	400	11.41	1	11.41	0.50	5.7
2.23	ILP-5 (CUSTOMER ROOM) SUPPLY-2	400	3.37	1	3.37	0.50	1.7
2.24	OLP-1 (CONTROL BUILDING) SUPPLY-2	400	40.14	1	40.14	0.50	20.1
2.25	OLP-2 (CONTROL BUILDING) SUPPLY-2	400	50.88	1	50.88	0.50	25.4
2.26	HVAC POWER PANEL-1 (380kV GIS BUILDING) SUPPLY-2	400	87.10	1	87.10	0.50	43.6
2.27	HVAC POWER PANEL-2 (380kV GIS BUILDING) SUPPLY-2	400	87.10	1	87.10	0.50	43.6
2.28	HVAC POWER PANEL-3 (380kV GIS BUILDING) SUPPLY-2	400	87.10	1	87.10	0.50	43.6
2.29	HVAC POWER PANEL-4 (132kV GIS-1 BUILDING) SUPPLY-2	400	70.40	1	70.40	0.50	35.2
2.30	HVAC POWER PANEL-5 (132kV GIS-1 BUILDING) SUPPLY-2	400	70.40	1	70.40	0.50	35.2
2.31	HVAC POWER PANEL-6 (132kV GIS-2 BUILDING) SUPPLY-2	400	70.40	1	70.40	0.50	35.2
2.32	HVAC POWER PANEL-7 (132kV GIS-2 BUILDING) SUPPLY-2	400	70.40	1	70.40	0.50	35.2
2.33	HVAC POWER PANEL-8 (CONTROL BUILDING) SUPPLY-2	400	70.40	1	70.40	0.50	35.2
2.34	HVAC POWER PANEL-9 (CONTROL BUILDING) SUPPLY-2	400	150.00	1	150.00	0.50	75.0
2.35	HVAC POWER PANEL-10 (CUSTOMER ROOM) SUPPLY-2	400	30.00	1	30.00	0.50	15.0
2.36	HVAC CONTROL PANEL-1 (380kV GIS BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.37	HVAC CONTROL PANEL-2 (380kV GIS BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.38	HVAC CONTROL PANEL-3 (380kV GIS BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.39	HVAC CONTROL PANEL-4 (132kV GIS-1 BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.40	HVAC CONTROL PANEL-5 (132kV GIS-1 BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.41	HVAC CONTROL PANEL-6 (132kV GIS-2 BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.42	HVAC CONTROL PANEL-7 (132kV GIS-2 BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.43	HVAC CONTROL PANEL-8 (CONTROL BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.44	HVAC CONTROL PANEL-9 (CONTROL BUILDING) SUPPLY-2	400	15.00	1	15.00	0.05	0.8
2.45	HVAC CONTROL PANEL-10 (CUSTOMER ROOM) SUPPLY-2	400	10.00	1	10.00	0.05	0.5
2.46	125V DC BATTERY CHARGER-2 (380kV GIS SYSTEM)	400	106.25	1	106.25	0.50	53.1
2.47	125V DC BATTERY CHARGER-4 (132kV GIS SYSTEM)	400	87.50	1	87.50	0.50	43.8
2.48	48V DC BATTERY CHARGER-2 (COMMUNICATION ROOM)	400	33.60	1	33.60	0.50	16.8
2.49	COOLING FAN SUPPLY – SGT-1 SUPPLY-2	400	46.35	1	46.35	0.50	23.2
2.50	COOLING FAN SUPPLY – SGT-2 SUPPLY-2	400	46.35	1	46.35	0.50	23.2
2.51	COOLING FAN SUPPLY – SGT-3 SUPPLY-2	400	46.35	1	46.35	0.50	23.2
2.52	COOLING FAN SUPPLY – SGT-4 SUPPLY-2	400	46.35	1	46.35	0.50	23.2
2.53	COOLING FAN SUPPLY – SGT-5 SUPPLY-2	400	46.35	1	46.35	0.50	23.2
2.54	COOLING FAN SUPPLY – SGT-6 SUPPLY-2	400	46.35	1	46.35	0.50	23.2
2.55	63A, GAS FILLING RECEPTACLE (380kV GIS)	400	30.92	1	30.92	0.00	0.0
2.56	63A, GAS FILLING RECEPTACLE (380kV GIS)	400	30.92	1	30.92	0.00	0.0
2.57	63A, GAS FILLING RECEPTACLE (380kV GIS)	400	30.92	1	30.92	0.00	0.0
2.58	63A, GAS FILLING RECEPTACLE (380kV GIS) (FUT.)	400	30.92	1	30.92	0.00	0.0
2.59	63A, GAS FILLING RECEPTACLE (132kV GIS-1)	400	30.92	1	30.92	0.00	0.0
2.60	63A, GAS FILLING RECEPTACLE (132kV GIS-1)	400	30.92	1	30.92	0.00	0.0
2.61	63A, GAS FILLING RECEPTACLE (132kV GIS-1)	400	30.92	1	30.92	0.00	0.0
2.62	63A, GAS FILLING RECEPTACLE (132kV GIS-2)	400	30.92	1	30.92	0.00	0.0
2.63	63A, GAS FILLING RECEPTACLE (132kV GIS-2)	400	30.92	1	30.92	0.00	0.0
2.64	63A, GAS FILLING RECEPTACLE (132kV GIS-2)	400	30.92	1	30.92	0.00	0.0
2.65	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
2.66	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
2.67	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
2.68	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
2.69	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
2.70	63A, GAS FILLING RECEPTACLES FOR OUTDOOR GIB	400	30.92	1	30.92	0.00	0.0
2.71	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 380kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
2.72	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 380kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
2.73	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 132kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
2.74	63A, RECEPTACLE FOR GAS FILLING/WELDING AT 132kV GANTRY AREA	400	30.92	1	30.92	0.00	0.0
2.75	63A, WELDING RECEPTACLE FOR POWER TRANSFORMER SGT-4	400	30.92	1	30.92	0.00	0.0
2.76	63A, WELDING RECEPTACLE FOR POWER TRANSFORMER SGT-5	400	30.92	1	30.92	0.00	0.0
2.77	63A, WELDING RECEPTACLE FOR POWER TRANSFORMER SGT-6	400	30.92	1	30.92	0.00	0.0
2.78	63A, WELDING RECEPTACLE FOR REACTORS	400	30.92	1	30.92	0.00	0.0
2.79	63A, WELDING RECEPTACLE FOR SST-2	400	30.92	1	30.92	0.00	0.0
2.80	63A, WELDING RECEPTACLE FOR PACU 1B (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
2.81	63A, WELDING RECEPTACLE FOR PACU 2B (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
2.82	63A, WELDING RECEPTACLE FOR PACU 3B (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
2.83	63A, WELDING RECEPTACLE FOR PACU 4B (132kV GIS-1 BUILDING)	400	30.92	1	30.92	0.00	0.0
2.84	63A, WELDING RECEPTACLE FOR PACU 5B (132kV GIS-1 BUILDING)	400	30.92	1	30.92	0.00	0.0
2.85	63A, WELDING RECEPTACLE FOR PACU 6B (132kV GIS-2 BUILDING)	400	30.92	1	30.92	0.00	0.0
2.86	63A, WELDING RECEPTACLE FOR PACU 7B (132kV GIS-2 BUILDING)	400	30.92	1	30.92	0.00	0.0
2.87	63A, WELDING RECEPTACLE FOR PACU 8B (CONTROL BUILDING)	400	30.92	1	30.92	0.00	0.0
2.88	63A, WELDING RECEPTACLE FOR PACU 9B (CONTROL BUILDING)	400	30.92	1	30.92	0.00	0.0
2.89	63A, WELDING RECEPTACLE FOR PACU 10B (CUSTOMER ROOM)	400	30.92	1	30.92	0.00	0.0
2.90	HV TEST SOCKET (380kV GIS BUILDING)	400	30.92	1	30.92	0.00	0.0
2.91	HV TEST SOCKET (132kV GIS-2 BUILDING)	400	30.92	1	30.92	0.00	0.0
2.92	PORTABLE CHARGER-2 (125V DC BATTERY CHARGER-2)	400	29.42	1	29.42	0.00	0.0
2.93	PORTABLE CHARGER-4 (125V DC BATTERY CHARGER-4)	400	29.42	1	29.42	0.00	0.0
2.94	SDB-10 (EXTERNAL TELECOM SHELTER) SUPPLY-2	400	8.00	1	8.00	0.50	4.0
2.95	VENTILATION CONTROL PANEL (380kV GIS BUILDING) SUPPLY-2	400	25.00	1	25.00	0.05	1.3
2.96	VENTILATION CONTROL PANEL (132kV GIS-1 BUILDING) SUPPLY-2	400	50.00	1	50.00	0.05	2.5
2.97	VENTILATION CONTROL PANEL (132kV GIS-2 BUILDING) SUPPLY-2	400	50.00	1	50.00	0.05	2.5
2.98	VENTILATION CONTROL PANEL (CONTROL BUILDING) SUPPLY-2	400	50.00	1	50.00	0.05	2.5

Load Summary

Description	Value
Total load at MDB	1698.1 kW
Total load at MDB in kVA	1997.8 kVA
The simultaneous peak load on Auxiliary Transformer excluding Oil Filtration Socket (80% of the AUX.TXFR. rating)	1997.8 kVA
Load of Oil Filtration Socket in kVA	147.22 / 0.85 = 173.20 kVA
The simultaneous peak load on Auxiliary Transformer including Oil Filteration Socket	(1997.81 + 173.2) = 2171.0 kVA
Hence Selected Auxiliary Transformer rating	2500.0 kVA

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