Electricity + Control January 2019

DRIVES + MOTORS + SWITCHGEAR

Overview of the upgrade solution The existing systemmust remain operational while the new system is being installed. After much de- liberation it was decided to install the new drive wheels behind the existing system. In order to balance the forces on the conveyor sheave wheel tower, the angle of the conveyor cables from un- derground should be similar to the angle descend- ing to the drive house. The drive wheels have to be placed as close as possible to the existing system. The inherit requirements of the new system are: • Speed matching of the conveyor ropes. • Fail safe braking systems. • ‘Soft’ starting of the conveyor. The customer also wished to achieve the following objectives: • A level of redundancy with respect to the main equipment to reduce down time. • Safety required: o Anti roll back on conveyor. o Safety guards with gate interlocks to trip conveyor if breached. • Lower conveyor speed until conveyor tail take- up has occurred. • Be able to utilise both the old and new drive wheel installations. System calculations From the source information and gearbox ratio, the following was calculated:

A single SCADA station will be used to control the plant. A main desk is installed as a maintenance location.

Figure 3: Drive wheel and idler wheel.

To increase redundancy with the braking system, the following will be implemented: • Dual hydraulic braking lines. • Four low speed brakes on each drive wheel (top two on one braking line, bottom two on the other hydraulic braking line). • High speed brakes on a disk between the mo- tor and gearbox (north and south). The brakes used are: • Brake stands (drive wheel) – Svendborg brakes BSFI 3120 96 kN brake force. • High speed brakes – Svendborg BSHF 330 24 kN brake force. Planetary gearboxes have been chosen because of their highest known torque density superiority. The down side of using planetary gearboxes is having to add gearbox coolers. Anti roll back devic- es will be installed into both gearboxes. Electrical solution The main components are: • New 3.3 kV switchgear – completely replacing the existing switchgear. • Drive transformers – double secondary windings DyN11 & Dd0 – 30 degrees phase shift to reduce harmonics – 3 MVA, 3.3 kV / 0.69 kV – two trans- formers will be installed for redundancy. • Drive change-over panels for swopping drive transformers. • NewMCC transformers 350 kVA, 3.3 kV/0.4 kV Dyn11 – two transformers will be installed for redundancy. • Variable speed drives – Sinamics G150 900 kW with braking resistors – two drives. • MCC – two Incomers – only one Incomer ACB will be installed – swop position to the other cradle to change transformer supply. Detailed information on variable speed drives and speed control: • Two parallel converters per drive – one con- nected to the star winding of the transformer

1 Rope pull per side (full load)

17.5 tons

2 3

Accelerating power

141.6 kW 567.5 kW

Power required for load

4 Power (friction) (5% of load)

28.4 kW

5 6

Drive size - required

737.6 kW 900.0 kW

Actual drive size

The following equipment will be installed: • Gearbox: Ratio – 89.75; Torque – 684 kN.m. • Motor: Dual winding – 790 kW; Four pole – 690V. • Variable speed drives: 900 kW, 690 V. Mechanical solution The drive wheel and idler wheel dimensions have been matched exactly, as have the relative posi- tions between the drive wheel and idler wheel to achieve the same wrap angle. The JVL lining on the drive wheels is identical to the existing sys- tem, alternating with polyester and aluminium.

Electricity + Control

JANUARY 2019

15