Siemens Robicon GH180 Perfect Harmony Medium Voltage Drives Applications in New Dry Process Cement Plants

The total installed capacity of the plant's fans is approximately 12,707–13,787 kW, accounting for about 34.8–37.7% of the plant's total installed power (33,500 kW), and their power consumption accounts for about 30%–40% of the plant's total electricity consumption. With the increasing adoption of roller mill systems, fan power consumption accounts for an even larger share.

The proportion of total power consumption is also increasing. Fans are designed for full-load conditions, but in actual production, changes in operating conditions and output will cause random adjustments in airflow and pressure. As is well known, fans are square-law loads; therefore, if...

By replacing the fan's drive system with an AC speed control system, and adjusting the motor speed to meet the airflow and pressure requirements under different operating conditions, energy consumed by baffles and valves can be saved. The energy-saving potential and effect are considerable.

Statistics show that a cement plant with a daily clinker production of 5,000 tons includes exhaust fans for waste gas treatment, high-temperature fans at the kiln tail, cooling fans for the grate cooler, exhaust fans for the cooler, and fans for the coal mill system, mainly used for system ventilation and heat exchange, with an installed capacity of 6407~

If the 7487kW unit were replaced with an AC speed control system, based on general usage experience, approximately 6.4 million kWh of electricity could be saved, resulting in annual electricity cost savings of 3.2 million yuan. The investment in the variable frequency speed control equipment could be recovered in about two years.

I. Overview

The cement industry is a major energy consumer, facing the arduous task of energy conservation and emission reduction. This is especially true with the increasing scale of modern dry-process cement production lines, which offer greater potential for energy saving. For example, a cement plant producing 5,000 tons of cement clinker per day...

The plant's installed capacity of blowers is approximately 12,707–13,787 kW, accounting for about 34.8–37.7% of the plant's total installed power (33,500 kW), and its power consumption accounts for about 30%–40% of the plant's total power consumption. With the increasing adoption of roller mill systems, the power consumption of blowers accounts for an even larger proportion of the total power consumption.

The proportion of electricity consumption is also increasing. Fans are designed for full-load conditions, but in actual production, changes in operating conditions and output will cause random adjustments in air volume and pressure. As is well known, fans are square-law loads; if the air volume is...

By replacing the machine's transmission system with an AC speed control system, and adjusting the motor speed to meet the air volume and air pressure requirements under different operating conditions of the fan, energy consumed by baffles and valves can be saved. The energy-saving potential and effect are considerable, according to statistics.

A cement plant with a daily clinker production of 5,000 tons includes exhaust fans for waste gas treatment, high-temperature fans at the kiln tail, cooling fans for the grate cooler, exhaust fans for the cooler, and fans for the coal mill system, mainly used for system ventilation and heat exchange, with an installed power of 6407–7487 kW.

If an AC speed control system is used instead, based on general usage experience, approximately 6.4 million kilowatt-hours of electricity can be saved, resulting in annual electricity cost savings of 3.2 million yuan. The investment in the frequency converter equipment can be recovered in about two years. This will play a significant role in reducing cement costs and improving the economic efficiency of enterprises.

Currently, newly designed dry-process cement production lines have adopted variable frequency speed control for key systems such as fans, pumps, grate coolers, air classifiers, various weighing equipment, and plate feeders. Furthermore, under the general trend of energy conservation and environmental protection, major domestic cement groups...

To implement energy conservation and emission reduction, electrical upgrades are being expedited for high-temperature fans and exhaust fans. For example, dozens of cement clinker production lines with a daily output of 5,000 tons under the Conch Group and Shanshui Group are undergoing upgrades to the drive systems of their kiln tail exhaust fans.

These groups, after thorough comparison, all ultimately chose Siemens Robicon high-voltage frequency converters from Siemens AG, which were originally used for speed regulation via hydraulic couplings, to upgrade to variable frequency speed control systems. Siemens Robicon frequency converters use multiple low-voltage units connected in series to form a drive...

The most significant feature of the high-voltage output structure of the dynamic system is that it achieves a perfect input waveform without the need for a filter; it also requires no external filter and has an almost perfect sine wave output, with both its input and output harmonic currents meeting the most stringent requirements.

The Siemens Robicon brand high-voltage frequency converters conform to the IEC 591 standard and are therefore also known as Perfect Harmony Medium Voltage Drives . This is crucial for large enterprises, as it avoids pollution to the public power grid and does not affect the normal operation of other large drive equipment within the company.

Okay. Because the main circuit structure of the frequency converter is simple and straightforward, without additional input/output filters, power factor compensators, step-up transformers, or other auxiliary circuits, the inverter power devices use simple and reliable IGBT power devices. Meanwhile, in the system structure...

In terms of design, it integrates the isolation transformer and frequency converter, including the control unit and various signal modules, into one unit, making installation, wiring, startup, and commissioning quick and simple. The mean time between failures (MTBF) of the entire system reaches 100,000 hours. The Siemens Robicon frequency converter also features...

The option includes a power cell bypass function, allowing the inverter to continue operating at full load even in the event of a power cell failure, thus ensuring extremely high reliability. Siemens SINAMICS PERFECT HARMONY GH180 Robicon VFDs offer voltage ratings from 2.3kV to 13.8kV and power ratings from [missing information - likely a power rating].

The range is from 225kW to 120,000kW, and it is currently widely used in my country's power, metallurgy, oil and gas, water treatment and other industries.

II. Regarding high-voltage frequency converters

Inverters that output voltages from 3KV to 13.8KV are called high-voltage inverters, or medium-voltage inverters abroad, and high-voltage inverters domestically. High voltage is mainly used in contrast to low-voltage inverters. The commonly used voltage level in China is 3300V.

4160V and 6000V can be classified in three ways:

By output voltage method:

High-voltage type: Direct high voltage output, no step-up transformer required for inverter output.

High-low-high type: A low-voltage frequency converter is used in the middle, and a step-up transformer is used at the end.

According to the type of intermediate link

Voltage source: The intermediate DC link is a capacitor.

Current source: The intermediate DC link is an inductor

According to the inverter circuit structure type

Three-level (center point clamping)

GTO/SGCT Current Source Inverter

    The Power Cell voltage series structure, with perfect harmonic-free operation, is the basis of the Siemens Robicon high-voltage frequency converter.

A typical high-voltage frequency converter topology consists of three parts: a rectifier circuit that converts the input AC to DC; a DC link in the middle, used for filtering and energy storage; and an inverter circuit that converts the DC back to AC and adjusts the output voltage or current.

The inverter coordinates and controls the current and frequency. A typical inverter has five independent components: input filter, power factor compensation, isolation transformer, inverter unit, and output filter. Because Siemens Robicon high-voltage inverters have good input/output characteristics,

Its main components are only an isolation transformer and a frequency converter.

III. Structural Principles and Performance Indicators of Siemens Robicon High Voltage Frequency Converters

　　The Siemens Robicon 6kV high-voltage frequency converter is based on the Power Cell voltage series structure. The frequency converter input is a three-phase AC voltage, and the voltage level can be selected. It can be connected in star or delta configuration, and the output is 6kV to 7.2kV. It can be directly connected to a three-phase induction motor.

1. Input harmonics and rectifier circuit

According to the national standard GB/T14549-93, for voltage, the total harmonic distortion (THD) of 6kV and 10kV power grids is required to not exceed 4%. For current, under the condition of a reference short-circuit capacity of 100MVA, the amplitude of each harmonic current is specified.

Specifically, for a 6kV power grid, the percentage conversion of each harmonic is approximately 4%. Excessive harmonics will cause additional harmonic losses in components of the public power grid, leading to malfunctions in relay protection and automatic devices, and affecting various electrical equipment.

Normal operation. According to the input harmonic standard and by comparing various rectifier circuits, the following conclusion can be drawn: the rectifier circuit must have at least 18 pulses (including 18 pulses) to meet the input harmonic standard.

    The Siemens Robicon 6kV high-voltage frequency converter uses a 36-pulse diode rectifier circuit. This multi-stage design achieves multi-pulse rectification, effectively eliminating input harmonics. Harmonic distortion is minimal, with input harmonic current distortion less than 2%.

The harmonics are far below the specified standards and will not affect the power grid without the use of filters.

2. Input power factor

The input power factor of a frequency converter is mainly related to the DC link (voltage source type or current source type) in the intermediate stage of the frequency converter.

In a voltage-source DC-DC converter, the capacitor provides the reactive current required by the motor, eliminating the need for grid exchange. This results in a high input power factor for the inverter, which remains essentially constant across the entire speed range. In a current-source DC-DC converter, the large...

Inductors require reactive current from the motor, which must be exchanged with the grid, resulting in a low power factor that decreases as the motor load decreases. Siemens Robicon high-voltage frequency converters, with an input power factor greater than 0.95, improve the quality of the power grid system and enhance grid transmission efficiency.

Total power factor on the input side.

3. Output harmonics and inverter circuit

The output waveform of a frequency converter includes parameters such as output harmonics, dv/dt, and common-mode voltage. The output waveform is closely related to the structure of the frequency converter inverter. The Siemens Robicon high-voltage frequency converter uses Power Cell voltage-series multi-level phase-shift PWM.

For voltage source inverters, a 13-level PWM voltage source type is used for the 6KV input inverter. The inverter power device in the Power Cell of Figure 2 uses IGBTs, which are simple to drive, mature and reliable, and have low drive power. Other models of high-voltage frequency converters require different inverter power devices.

Using 6500V high-voltage IGCT or high-voltage IGBT requires complex driving, high driving power, and expensive and difficult-to-purchase spare parts.

Harmonic components in the inverter's output waveform can cause additional heating and torque pulsation in the motor, and the output dv/dt and common-mode voltage can affect the motor's insulation. The waveform output by the Siemens Robicon high-voltage inverter is very similar to a sine wave, and...

With a small dv/dt amplitude of approximately 900V, no output filter is needed, and the inverter can directly output 6000VAC, allowing the use of existing, older, domestically produced asynchronous motors. In most domestic applications, 6KV older domestically produced motors are used, many of which have insulation ratings that are...

It is a Class B standard, which is feasible for the AC drive technology upgrade of cement plants, and does not require the replacement of the motor.

To ensure the reliable operation of Siemens Robicon high-voltage frequency converters, a redundant structure is incorporated, with an optional power cell bypass function. Even in the event of a power cell failure, the converter can still operate at full load, demonstrating extremely high reliability. This includes input frequency conversion...

When the system, including the transformer and frequency converter, is fully loaded, its efficiency can reach 97% and the noise is less than 75dB.

    Siemens Robicon high-voltage frequency converters feature extremely flexible communication capabilities. In addition to standard input/output signal interfaces, they can also connect to a personal PC via RS485 or a standard Ethernet port for configuration and control.

It also supports multiple communication protocols, such as PROFIBUS DP, Device Net, Modbus Plus, etc.

IV. Conclusion

1. To implement energy conservation and emission reduction, large cement groups are accelerating plans to upgrade the electrical systems of high-temperature fans and exhaust fans. Given the high initial investment, it is advisable to proceed with upgrades as needed, starting with the process fans in the kiln system. The author suggests proceeding with these upgrades first.

The modification of the kiln tail exhaust fan drive system involves replacing the hydraulic coupling speed regulation with variable frequency speed regulation. Since the roller mill system's fans have a large capacity and relatively stable airflow and pressure variations during operation, it is recommended to postpone their modification.

2. When selecting a high-voltage frequency converter, the performance-price ratio of various brands should be compared repeatedly. Reliability should be the top priority in terms of performance, followed by input and output waveforms, with harmonics below national standards. As for the number of output lines...

Cables, etc., should not be the main indicators.

3. In the cement industry, rotary kilns have used DC drives for over a century, primarily due to the high requirements for their starting torque, typically 2.5 times the rated torque. Additionally, they require long overload capacity time and high overload ratios. Currently, some EPC projects also...

The rotary kiln is required to use AC variable frequency drive. However, I do not recommend converting the rotary kiln to AC variable frequency drive for energy saving. If such a conversion is necessary, the overload capacity must be carefully considered, and the variable frequency device must be carefully selected.