A Brief Discussion on the Design of a New American-Style Box-type Substation for Wind Power Generation

Dyson

Field: Electrical Standards

China

Introduction

As a clean and renewable energy source, wind energy has increasingly attracted the attention of countries around the world. Its reserves are enormous. The total global wind energy resources amount to approximately 2.74×10⁹ MW, of which the exploitable wind energy is 2.0×10⁷ MW. In China, wind energy reserves are large, widely distributed, and the potential for development and utilization is huge.

Wind power generation has developed rapidly in recent years, and the box - type substations used in conjunction with it are mostly American - style box - type substations (hereinafter referred to as wind - power American - style substations).

Currently, the conventional wind - power American - style substations for wind power generation are of the "one - machine - one - substation" type, that is, one wind turbine (hereinafter referred to as wind turbine) is equipped with one wind - power American - style substation. With this configuration, when the wind speed in the wind farm is very low, the wind turbine will operate under - loaded, easily causing waste of wind turbine resources. In March 2010, our company designed 31 new - type "two - machines - one - substation" wind - power American - style substations for a certain wind farm in Inner Mongolia, that is, two wind turbines are equipped with the same wind - power American - style substation.

Determination of Substation Technical Parameters

Product Model: ZCSF - Z.F - 1000/36.75/0.69/0.4
Rated Capacity
- High - voltage: 1000kVA
- Low - voltage 1: 820kVA
- Low - voltage 2: 180kVA
Rated Voltage
- High - voltage: 36.75kV
- Low - voltage 1: 0.69kV (The rated capacity of the corresponding wind - power American - style substation is 820kVA, and the corresponding wind turbine power is 750kW)
- Low - voltage 2: 0.4kV (The rated capacity of the corresponding wind - power American - style substation is 180kVA, and the corresponding wind turbine power is 160kW)
Connection Group: Dyn11yn11
Tap Range: ±2×2.5%
Short - Circuit Impedance: 7% (Under rated voltage and frequency, based on the half - through impedance of the rated capacity of the high - voltage winding)
Rated Current
- High - voltage: 15.71A
- Low - voltage 1: 686.1A
- Low - voltage 2: 259.8A3

Working Principle and Schematic Diagram of the Substation

After contacting the design institute and the wind turbine manufacturer, it was determined that they required 31 three - phase, combined - type, common - tank, split - type, terminal - type American - style box - type substations. The transformer in these substations needed to have a low - voltage double - split structure, and the voltages of the two low - voltage sides were not equal.

Working Principle: The user installed two wind turbines with unequal powers on the same shaft. Wind turbine 1 is a synchronous wind turbine with a power of 750kW and a rated voltage of 690V; Wind turbine 2 is an asynchronous wind turbine with a power of 160kW and a rated voltage of 400V. The user installed a device for each wind turbine to automatically select the wind turbine according to the wind speed in the wind farm. This device can automatically choose which wind turbine to use based on the wind speed.

The box - type substation can output corresponding capacities according to the three different powers of the wind turbines. When the wind speed is very low, the 160kW wind turbine with a small power is selected for operation, and the output capacity of the substation at this time is 180kVA; when the wind speed is relatively high, the 750kW wind turbine with a large power is selected for operation, and the output capacity of the substation is 820kVA; when the wind speed is very high, both wind turbines are selected for operation simultaneously, and the output capacity of the substation at this time is the full capacity of 1000kVA. For this purpose, the transformer was designed into an axially double - split "low - high - low" structure. The 690V low - voltage winding is sleeved on the innermost side, the high - voltage winding is in the middle, and the 400V low - voltage winding is sleeved on the outermost side. Each wind - power American - style substation consists of a transformer room, a high - voltage cable room, and a high - and low - voltage operation room. In the low - voltage operation room, one 690V and one 400V low - voltage circuit breaker are installed respectively, which can control their respective low - voltage sides, equivalent to having two low - voltage operation rooms.

The schematic diagram of the substation's working principle is shown in Figure 1.

Application Effects of the Substation

Since the user can automatically select wind turbines of different powers according to the wind speed, this can completely solve the problem of waste of wind turbine resources and save energy.
The user can purchase one less substation (compared with the "one - machine - one - substation" model), which is beneficial for wind - power American - style substations to minimize the user's upfront investment cost in the wind farm and improve the utilization efficiency of resources.
The transformer adopts a "low - high - low" structure, which increases the short - circuit impedance of the substation. Consequently, it can effectively restrict the short - circuit current and boost the operational reliability of the substation.