Mechanical Technology

Mechanical Technology — July 2015

⎪

Power transmission, bearings, bushes and seals

⎪

wo of Europe’s largest synchro-

nous motors, along with the

highest power-rated medium

voltage (MV) drives ever used

in a reversing roughing mill, have been

commissioned by ABB at Tata Steel’s

Port Talbot hot strip mill in South Wales.

The replacement motors and drives

were the focus of a major £25-million

reversing roughing upgrade – a key part

of the rolling process which transforms

a 23 cm thick slab of red-hot steel into

sheet, less than 3.5 cm thick, before

further reducing it to produce hot rolled

strip. The upgrade aims to significantly

increase steel production while improving

final product quality.

The reversing rougher is a heavy

torque application and as such demands

two ABB 12.5 MW salient pole synchro-

nous motors, together with two ABB

MV drives rated at 36 MVA at 3.1 kV,

to power the slab between a set of rolls.

Previously, two 6.0 MW direct current

(dc) motors, installed in 1985, were

operated some 30% over their intended

capacity. The overload regularly stressed

the windings, making the motors difficult

to maintain and subject to potential

catastrophic failure. Although operating

in overload the roughing mill was still the

bottleneck process for 50% of the time,

putting a hard limit on plant output.

The new synchronous motors give

Europe’s largest motors and drives

power steel roughing mill

ABB has commissioned two of Europe’s largest synchronous motors

and medium voltage drives at the roughing mill at Tata Steel’s hot

strip mill in Port Talbot, South Wales.

Left:

Two of Europe’s largest synchronous motors ever used in a reversing roughing mill have been commissioned by ABB at Tata Steel’s Port Talbot hot strip

mill in South Wales.

Right:

The upgrade aims to increase steel production significantly while improving final product quality.

the response demanded while the

ACS6000 MV drives with their motor

control platform that uses direct torque

control (DTC), provide unrivalled speed

and torque control. As the slab enters the

reversing rougher there is no perceived

speed drop, as happened with the dc mo-

tors. The new motors and drives control

the slab precisely, with no over shoot in

speed. This results in the slab being pro-

cessed much faster and reduces unneces-

sary torque reversals in the mechanical

drive train. The slow control of the dc

motors caused severe torque swings in

the drive train, resulting in fatigue cycling

to the mechanical equipment. This no

longer occurs, resulting in a much quieter

and safer operating environment, with

improved production capacity together

with increased reliability.

“With the old system, the average

cycle time was 95 seconds. Today, it is

80 seconds,” says Steve Winkley, Tata

Steel’s project manager for the roughing

mill project. “When we change direction

of the bar, it’s much faster than ever

before. When we take advantage of the

motors maximum top speed, this will

result in an average production speed

increase of 30 t per hour – that is a

staggering 200 000 t per year. This sig-

nificant increase in production is almost

a side effect of having to replace the dc

machine. We successfully turned what

was a potentially catastrophic situation

with the overloaded dc motors into an

unprecedented success, breaking a series

of ‘all time’ production records.”

For reversing roughing mills, reliability

is paramount. ABB’s extensive experi-

ence of mill applications together with

proven design technology and manufac-

turing know-how combined with thor-

ough quality control and comprehensive

testing throughout the production cycle,

combined to make Tata Steel’s decision

to use the company easier.

Tata Steel meticulously structured

the shutdown of the existing facility;

a process of design, planning and risk

management that began back in 2011.

This risk mitigation strategy lead to some

90% of the installation being completed,

commissioned and tested before the

plant shutdown.

Over a four-week period, starting

in August 2014, the plant completely

closed for what was to be the most

intense upgrade in 25 years. The old

motors and spindles were removed and

the foundation for the new equipment

prepared. The pre-assembled new mo-

tors were then lifted into position at the

same time that the new spindle system

was being installed. The two motors were

connected with the spindle system and

all the pre-installed and

commissioned

services and control equipment was

connected ready to run the new motors.

“It’s fantastic to see the installation

progress to schedule and really justifies

the approach we took on this project with

90% of equipment pre-installed before

shut down,” says Winkley.

“We are really happy with ABB, in

terms of the equipment and the compa-

ny; both performed absolutely brilliantly,”

he concludes.