Step-up transformer stations for energy storage

Brunstock’s step-up skid stations contain power transformers and switchgear for battery energy storage plants. These modular substations convert low-voltage AC power generated by the power conversion system (PCS) into medium-voltage AC power and feed it into the power grid.

This step-up transformer skid station integrates a ring main unit, a transformer, a power converter system and an auxiliary power supply. Installed on a steel skid, this unit has a strong foundation and can withstand outdoor elements. This highly integrated power transformer and voltage conversion solution is ideal for energy storage plants in medium-voltage grid-tied applications.

The modular design offers speed and commercial competitiveness while Brunstock also has the flexibility to cater for specific project needs. It is available with a central PCS or string layout.

Features of our energy storage step up stations

Intelligent

The station detects the operating status of its ring main unit, transformer and PCS in real time
The station displays power parameters online, with accurate current and voltage detection
Remote access to the running information of the complete step-up skid station
Remote control of the circuit breaker for the PCS and ring main unit (RMU)

Manufacture

Internal equipment is selected and installed
The 20-foot container size of the skid structure facilitates easy transportation and installation

Reliable

Solid and reliable structure design
IP54 rating of medium-voltage RMU room and PCS

Fast

Fast deployment can be implemented
Only PCS needs to be routed in and medium-voltage cables need to be routed out on site

Images of our step up skid station for BESS

Two common layout options for a step-up skid station for battery energy storage: central PCS and string PCS

A step-up station for BESS, transformer kiosk

A step-up skid station for BESS with central PCS, open to elements, no enclosure

Step-up skid station with string type PCS, SF6-free, environmentally friendly

Components of a Brunstock energy storage step up station

BGS-12 a 12kV ring main unit (RMU) made for electrical kiosks (substations) by Brunstock.

Application of energy storage step up transformer stations

Network application of Brunstock’s step-up skid station for BESS

A diagram showing the components of a step-up station for BESS in a power network.

Diagram example of step-up skid station with central PCS

A diagram showing a possible network layout or configuration of a step-up station with central PCS for a battery energy storage system.

Diagram example of step-up skid station with string PCS

A diagram of a BESS step-up station with a string layout in its PCS

A diagram of a step-up transformer station attached to four BESS batteries.

A diagram of many step-up transformer stations attached to BESS batteries.

Appearance of Brunstock’s step up station for energy storage

Exterior dimensions

For ease of transportation, the station has the same dimensions as a 20-foot container: W 6,058mm x H 2,896mm x D 2,438mm.

Internal composition

Technical data

Power transformers for energy storage – technical data

Type	3,000kVA	5,000kVA
Transformer type	Oil transformer	Oil transformer
Rated power	3,000kVA @ 40C (see note 1)	5,000kVA @ 40C (see note 1)
Max. power	3,400 kVA @ 30C	5,500 kVA @ 30C
Vector group	Dy11	Dy11y11
LV/MV voltage	0.8kV / 20-35kV	0.8kV / 0.8 kV / 20-35kV (see note 2)
Maximum input current at nominal voltage	2,500 A x 1	2,500 A x 2
Frequency	50Hz	50Hz
Tapping on HV	0, ±2x2.5%	0, ±2x2.5%
Efficiency	≥99%	≥99%
Cooling type	ONAN (Oil Natural Air Natural)	ONAN (Oil Natural Air Natural)
Impedance	6.5% (±10%)	6.5% (±10%)
Oil type	Mineral oil (PCB free)	Mineral oil (PCB free)
Winding material	AI/AI	AI/AI
Insulation class	A	A

MV switchgear for energy storage – technical data

Type	3,000kVA	5,000kVA
Insulation type	Gas SF6-free
Rated voltage	24-36kV (see note 2)	24-36kV (see note 2)
Rated current	630A	630A
Internal arcing fault	IAC AFLR 31.5 kA/1s	IAC AFLR 31.5 kA/1s
Qty of feeder	2-3 feeders	2-3 feeders
MV surge arrester for VCB	Optional (see note 3)	Optional (see note 3)

PCS for energy storage – technical data

Type	3,000kVA	5,000kVA
DC side	800V-1500V, 1935A x 2	1300V-1500V, 2154A x 2, 2 inputs
AC side	3000kVA/690V	5000kVA/900V

Protection equipment for energy storage – technical data

AC input protection	Circuit breaker	Circuit breaker
DC side	800V-1500V, 1935A x 2	1300V-1500V, 2154A x 2, 2 inputs
Transformer protection	Oil-temperature, oil-level, oil-pressure	Oil-temperature, oil-level, oil-pressure
Relay protection	50/51, 50N/51N	50/51, 50N/51N
LV overvoltage protection	AC Type II (optional: AC Type I +II)	AC Type II (optional: AC Type I +II)
Anti-rodent protection	C5-Medium	C5-Medium

General step up station – technical data

Type	3,000kVA	5,000kVA
Dimensions (WxHxD)	6,058mm x 2,896mm x 2,438mm	6,058mm x 2,896mm x 2,438mm
Approximate weight	≤5T	≤22T
Operating temperature range	-25C~60C (see note 4)	-25C~60C (see note 4)
Auxiliary power supply	100kVA/400V	100kVA/400V
2kVA UPS	Optional (see note 3)	Optional (see note 3)
Degree of protection	IP54	IP54
Allowable relative humidity range (non-condensing)	0-95%	0-95%
Operating altitude	1,000m (see note 5) standard, greater than 1,000m optional extra	1,000m (see note 5) standard, greater than 1,000m optional extra
Communication	RS485, Ethernet, Optical fiber	RS485, Ethernet, Optical fiber
Compliance	IEC 60076, IEC 62271-200, IEC 62771-202, IEC 61439-1, EN 50588-1	IEC 60076, IEC 62271-200, IEC 62771-202, IEC 61439-1, EN 50588-1

Notes:

1. For more details on AC power, please refer to the de-rating curve
2. Rated output voltage from 20 kV to 36 kV, more available upon request
3. Additional features are available, which the product doesn’t contain, by default, please discuss with your Brunstock rep
4. When ambient temperature ≥55C, an extension roof shall be equipped for the station on site by the end user
5. For higher operating altitude, please consult with Brunstock

Product design of our step up stations for energy storage

A photo of a step-up station power transformer

Schematic of a transformer in a step-up station for PV

A Brunstock step-up transformer station consists of three parts: PCS, transformer room, and medium-voltage room. This is mounted on a metal pad (a skid) or inside an enclosure that is the same size as a standard shipping container.

PCS

The PCS cabinet, located in the container or on the skid, is used to converge the DC power to AC power and feed it into the MV grid. It can be a central or string type of PCS, according to customer specifications. The size of each PCS influences the overall layout of
the container or skid station.

Medium voltage room

The medium voltage room contains a Brunstock Gas-insulated Secondary ring main unit and a circuit breaker. This transformer
protection is mainly achieved through the relay protection device. When the transformer is overloaded or short-circuited, the circuit breaker can be reliably disconnected. When the transformer experiences an overtemperature fault, heavy gas fault, or oil over pressure fault, the circuit breaker trips and the system is quickly protected.

View technical details of BGS-12

View technical details of BGS-40.5

The medium voltage room also contains a communication box and a power distribution cabinet.

Transformer room

The transformer room mainly includes a transformer that is used to convert the low-voltage AC power into medium-voltage AC power.
The transformer integrates accessories such as a pressure relief valve, tap changer, oil level indicator, pressure gauge, oil temperature
indicator, oil filling valve and oil drain valve.

The structure of 4,600kVA is shown in the figure as an example. The oil-cooled transformer adopts natural heat dissipation, and the top is not covered.

Step-up station for energy storage – technical data

Item	Type	4,600/33, 3 windings, oil-immersed
Rated output kVA	&ndsp;	4,600
Vector group	&ndsp;	Dy11y11
Type of cooling	&ndsp;	ONAN
Rated voltage kV	HV	33
Rated voltage kV	LV	0.8
Rated voltage	Voltage variation	±10%
Rated current A	HV	154
Rated current A	LV1	3,248
Rated current A	LV2	3,248
Number of phases		3
Rated frequency Hz		50
Frequency variation %		±5
Conductor materials	HV	Aluminium
Conductor materials	LV	Aluminium
Tap changer	LV	Off circuit
Tap changer	HV	±2x2.5%
Insulation level kV	HV	LI 170/AC 70
Insulation level kV	LV	AC 5

Notes:

1. For more transformer ratings, please consult your Brunstock rep

Thermal design

Considering different working conditions and requirements for each compartment and component, Brunstock’s step-up stations adopt
different cooling methods for different compartments:

The ingress protection level of the PCS cabinet is high, so it uses forced-air cooling to take away the heat inside the PCS cabinet
The MV transformer adopts ONAN mode
The MV switchgear and the communication & power distribution cabinet have natural cooling via vents, air intake from the bottom and air extraction by the fan, above

The science-based design of our step-up skid structure ensures cooling efficiency and effectively extends the service life of internal components and the entire station.