Electrical power supply transformer

powerdryimmersed

General description
Electric boosting has been used for many years in the glass industry. Initially most boosters were installed simply to increase furnace output. Today electric boosting can be utilised to give a number of benefits including increased output, improved glass quality and improved efficiency of the fossil fuel firing system.

Benefits

• Increased furnace output
• Improved and stable glass quality
• Improved efficiency of fossil fuel firing system
• Improved thermal gradients in the melter
• Reduced time for colour changes
• Increased furnace flexibility when changing furnace output (pull changes)

Types of booster systems
Each booster system is tailor made according to the furnace type and customer requirements. Glass Service offers systems including:

• Melting end booster to increase output
• Thermal barrier booster to stabilise convection currents
• Refining booster
• Throat booster for use during heat up and during low pull conditions

Scope of supply
Each booster system supplied by Glass Service can be provided as a stand alone system or integrated into the furnace control system. Equipment supplied for the electric booster includes:

• Power transformer(s)
• Control panel
• Electrodes and holders
• Electrode holder water cooling system
• Emergency air cooling
• Cables and connectors

Melting booster
When installed to increase furnace output, the melting booster can normally provide an additional ~30% over and above the glass melted by the fossil fuel firing. Electric boosters are recommended in coloured glass furnaces to maintain bottom temperature. Melting booster electrodes can be installed in furnace side walls or furnace bottom (bottom electrodes preferred to minimise side wall block corrosion). Typical installed power range is 400 to 1200 kVA, with larger systems possible depending on economics and electricity cost.

Thermal barrier booster
The barrier booster reinforces and fixes the convection current in the furnace at the hot spot and increases temperature in the front zone. The improved convection creates a barrier to the batch resulting in better batch cover and improved glass quality. Installed power can vary from 200 to 1000 kVA depending on furnace size and geometry. Driver technology is usually thyristors with dry transformer; in some cases a tap position changer (OLTC) is used. Connection is usually three phase with electrodes positioned for balanced phase load. Electrodes are molybdenum rods with water cooled holders. Barrier booster power is limited by furnace bottom temperature, glass temperature and electrode temperature.

Throat booster
Throat boosters are used for heating up the furnace throat or for temperature maintenance. Recommended for deep refiner furnaces and for coloured and special glasses. Installed power typically 30–70 kVA. Driver technology: thyristor and dry-transformer low voltage single phase (e.g. 400 Vac). Electrodes are molybdenum with water cooled holders.

Transformer technology
Power transformer technology depends on installation size. For smaller installations: thyristor technology with dry transformer. For larger installations: high voltage, oil-filled transformer with tap change switch (OLTC). OLTC features and typical characteristics include clean sinusoidal output, medium voltage input range (approx. 4,000–20,000 V), power range 400–1200 kVA, voltage output regulator with multiple steps (e.g. 21–29 steps), voltage output range ~80–300 V, various primary/secondary connection options, cooling types (ONAN or ONWF) and standard protections (Buchholz relay, oil temperature and water temperature control). OLTC advantages: long life, high energy efficiency, clean output waveform, reduced field cabling, long maintenance-free operation.

Circuit and drive types
Circuit type on-load tap position changer transformer (OLTC): clean sinusoidal wave output, long transformer life, high efficiency, no obsolescence. Circuit type thyristor unit (TU): used for low power boosters (30–400 kVA); cheaper to install than OLTC. TU features: input voltage range 220–600 Vac, output 80–300 Vac, power range 20–600 kVA per transformer, dry transformer with multi-voltage secondary selection and temperature sensor, continuous power regulation, various connection options (open/closed delta, special connections).

Control system
Glass Service provides a dedicated control system based on DCS (Honeywell HC900) able to manage OLTC or thyristor TU boosters. The control system manages:

• Power booster PID or current booster PID
• Voltage input
• Voltage output
• Current value for each electrode
• Temperature value for each electrode
• Earth current and voltage monitoring
• Water cooling monitoring for each electrode
• Transformer alarms and thyristor alarms
• Emergency condition strategies

The HMI can be a local touch screen panel or a central PC SCADA. All process parameters and variables are controlled and recorded for process analysis.

Water cooling
Each booster has a dedicated water cooling circuit to provide cooling water to electrode holders with a special flow control and monitoring system. Water flow is manually controlled; low flow or increased temperature is detected by sensors and pressure switches. Water flow switch is designed for high reliability and simple maintenance.

Electrode holders
Glass Service has developed a high reliability electrode holder for molybdenum electrodes. Key features include:

• Dual cooling circuit: primary water cooling and secondary/emergency air cooling
• Thermocouple (K type) for head temperature detection
• One-block machined head
• Laser welded tube cooling connections
• Max head temperature 1000°C; recommended operating head temperature max 800°C
• Cooling water consumption approx. 5 l/min
• Max cooling water temperature 35°C; operating pressure 2–4 bar
• Horizontal or vertical installation
• Holders supplied for electrode diameters including 1.50, 2.0, 3.0 and 4.0 inch
• Accessories: cooling tubes with high electrical resistance, mechanical supports and electrical insulation, emergency supports for bottom installation, water and air valves, fittings

Caractéristiques / spécifications techniques

• Electrode type: molybdenum rods
• Melting booster installed power: typically 400–1200 kVA (larger possible)
• Thermal barrier booster power: typically 200–1000 kVA
• Throat booster power: typically 30–70 kVA (single phase)
• Drive technologies: thyristor + dry transformer; OLTC (oil-filled transformer with on-load tap changer)
• Transformer input: medium voltage (approx. 4 kV–20 kV) for OLTC systems
• Transformer power range: typically 400–1200 kVA (OLTC), 20–600 kVA per transformer (TU)
• Voltage output range: approx. 80–300 V (depending on configuration)
• Phases: mostly three-phase (balanced load); throat boosters often single-phase
• Cooling: electrode holder water cooling + emergency air cooling; dedicated water circuit with flow/pressure/temperature monitoring
• Electrode holder ratings: cooling water consumption ~5 l/min; max head temp 1000°C; operating head temp max 800°C; cooling water pressure 2–4 bar; max water temp 35°C
• Control: DCS Honeywell HC900, HMI local or central SCADA; functions include PID control, monitoring of voltages/currents/temperatures, alarms and emergency strategies
• Installation: retrofit in operating furnace possible