Xylem Aquavar, Instruction Manual

Page: 57 / 172

Short-circuit protection
The adjustable frequency drive must be protected against short-circuit to avoid electrical
and fire hazard. We recommend using the fuses mentioned below to protect service
personnel and equipment in case of an internal failure in the drive. The adjustable
frequency drive provides full short-circuit protection in case of a short-circuit on the motor
output.
Overcurrent protection
Provide overload protection to avoid fire hazard due to overheating of the cables in the
installation. The adjustable frequency drive is equipped with internal overcurrent
protection that can be used for upstream overload protection (UL applications excluded).
See par. 4-18 Current Limit. Moreover, fuses or circuit breakers can be used to provide
the overcurrent protection in the installation. Overcurrent protection must always be
carried out according to national regulations.
Fuse and Line Power Disconnectors tables are listed in Section 10 :
Technical Specification.
5.14 Motor insulation and motor bearing currents
Motor insulation
For motor cable lengths ≤ than the maximum cable length listed in the General
Specifications tables, the following motor insulation ratings are recommended because
the peak voltage can be up to twice the DC link voltage, 2.8 times the AC line voltage due
to transmission line effects in the motor cable. If a motor has lower insulation rating, it is
recommended to use a du/dt or sine-wave filter.
Nominal AC Line Voltage Motor Insulation
U
N
≤ 420 V Standard U
LL
= 1300 V
420 V < U
N
≤ 500 V Reinforced U
LL
= 1600 V
500 V < U
N
≤ 600 V Reinforced U
LL
= 1800 V
600 V < U
N
≤ 690 V Reinforced U
LL
= 2000 V
Motor bearing currents
It is generally recommended that motors of a rating 150 hp [110 kW] or higher operating
via adjustable frequency drives should have NDE (Non-Drive End) insulated bearings
installed to eliminate circulating bearing currents due to the physical size of the motor. To
minimize DE (Drive End) bearing and shaft currents proper grounding of the drive, motor,
driven machine, and motor to the driven machine is required. Although failure due to
bearing currents is low and very dependent on many different items, for security of
operation the following are mitigation strategies which can be implemented.
Standard Mitigation Strategies:
1. Use an insulated bearing
2. Apply rigorous installation procedures
– Ensure the motor and load motor are aligned
– Strictly follow the EMC installation guidelines
– Reinforce the PE so the high frequency impedance is lower in the PE than the input
power leads.
– Provide a good high frequency connection between the motor and the adjustable
frequency drive for instance by shielded cable which has a 360° connection in the
motor and the adjustable frequency drive.
– Make sure the impedance from adjustable frequency drive to building ground is
lower than the grounding impedance of the machine. This can be difficult for
pumps. Make a direct ground connection between the motor and load motor.
5 Electrical Installation
Aquavar ® Intelligent Pump Controller - 150 HP to 600 HP INSTRUCTION MANUAL 55