Mains pollution: ac drive

The line currents of DC drives with a 6-pulse thyristor bridge will always contain, in addition to the fundamental wave, the 5th,
7th, 11th and 13th harmonics with empirical values of 22 %, 14 %, 9 %, 7.6 % , referenced to the fundamental wave. In the
case of several DC drives operating simultaneously on the mains, the different phase sequences of the harmonic currents will
produce a "statistical improvement" in the level of mains pollution.
Due to the dimensioning method adopted for the smoothing inductors, harmonic currents with contents of 40 %, 14 %, 9 %
and 7.6 % must be anticipated with AC drives featuring a 6-pulse diode bridge in 1-quadrant drives. Due to the identical phase
angle of the harmonic currents, several drives on the same mains can be regarded as one drive with the same total current.This
also applies for thyristor bridges in 4-quadrant operation.
Input bridges with IGBT switching elements enable the low-frequency harmonics to be substantially reduced, but conversely
create more high-frequency harmonics.

Reactive-power demand

Both drive concepts (AC and DC) take reactive power from the mains. Its size is negligible in the case of AC drives, and is RPMdependent below the rated speed with DC drives. The AC drive is the more favourable option here.
Values obtained from empirical feedback:
For AC drives, the value for cos ϕ
1
 is in
1-quadrant applications
with diode bridge cos ϕ
1
 ≈ 0.99
4-quadrant applications
with thyristor bridge and
with energy recovery into the mains cos ϕ
1
 ≈ 0.9
Values obtained from empirical feedback:
For DC drives, the value for cos ϕ
1
 is in
1-quadrant applications cos ϕ
1
 ≈ 0...0.9
4-quadrant applications cos ϕ
1
 ≈ 0...0.85

Modernization of existing DC drive

When it comes to the question of whether it is worth while
modernizing an existing DC drive or less expensive to replace
it entirely with an AC drive, there are also various arguments
which need to be assessed:
Basically, there are several options available for a modernization job:
1. Replace the entire DC drive (converter and motor) by a new
DC drive.
2. Replace only the converter cubicle, if the motor is still in
good condition.
3. Replace the converter module by a modern digital unit.
4. Replace the old, analog drive electronics by new, digital
electronics while continuing to use the power section
(recommended only for ratings above 1 MW).
5. Replace the entire drive system with a new AC drive.
When answering the question of what approach constitutes
the optimum solution in a particular case, the following main
criteria are important:
Will the requirements for the drive change in future (load
requirements, environmental conditions)?
In what condition are the individual components of the
system (reliability, age, maintenance outlay)?
How far will the supply conditions change in future?
Before a decision is made to modify a drive from DC to AC
design, the following points should be taken into consideration:
Outlay for new power cabling.
Space requirements for converter cubicles.
Dissipation of energy losses from the switchroom sufficient?
Foundations, mounting for motor sufficient?
Space requirement for new motor.
Duration of conversion work.

Price comparison DC and AC drive systems

(unit + motor or complete switchgear cabinet  + motor)
Based on the present-day development status of DC and AC drive engineering, and taking into account all the
systems' advantages/disadvantages mentioned above, the following guideline figures can be given:
1-quadrant drives <40...80 kW ê AC drives less expensive
4-quadrant drives >40...60 kW
(AC converter +  braking resistor; see Fig. 10); ê DC drives less expensive
Regenerative 4-quadrant drives > 15 kW ê DC drives less expensive

SIMOVERT MASTERDRIVES Motion Control

MASTERDRIVES MC is Migrating to the Siemens SINAMICS Family of drives

The Siemens Simovert MASTERDRIVES AC drive was introduced in 1994 and over 1 million units have been installed throughout the world. This very successful product will finally reach its maturity in October 2010. MASTERDRIVES will continue to be available and supported for several more years, but most customers should begin to familiarize
themselves with their options for spare parts or migration to the Siemens

Benefits of MASTERDRIVES MC

• Increased productivity and decreased project costs due to product reliability
• Proven track record
• Reduced maintenance
• Superior control performance
• Seamless integration into the automation environment

Key Attributes

Reliability

• Over 1,000,000 units installed worldwide in all types of applications and environments
• Global support
• Rated for UL and CSA international standards such as CE and NEMA

Flexibility

• Can be tailored to your specific application using on-board free-function blocks and integrated technology functions
• Seamless integration into automation hierarchy
• Platform design for a wide range of industrial voltages

Ease of Use

• Completely uniform from 1HP to 300HP
• Easy-to-connect, modular plug-in option boards for encoder evaluation solve every feedback task

Technical Data

MASTERDRIVES MC are available for a supply voltage of 3-phase 380 V to 480 V AC, 50/60 Hz, depending on the output, in the following types of construction

• Compact PLUS (0.55 - 37 kW) (0.75 - 50 HP)
• Compact Units (2.2 – 37 kW) (3 – 50 HP)
• Chassis Units (45 – 250 kW) (60 – 335 HP)
• Performance 2 (0.75 to 710 kW) (1000 HP)

Typical Applications

• Material handling – pick and place, bay racking
• Printing press – electronic line shafting
• Packaging – boxing, wrapping, bottling
• Textile winders/finishing
• Cut to length – pipe, board, precision plastic
• Wood finishing
• Winders – fabric, steel sheets, insulation
• Wire drawing
• Web handling – paper, fabric, insulation
• Converting machines
• Common DC bus
• Paper, textile, and plastic processing
• Rolling mills