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An operating frequency of 300 Hz
is to be recommended for a high-
frequency electric tool installa-
tion. The higher motor rotational
speed at 300 Hz is particularly
advantageous at today's circum-
ference velocities for grinders.
The increased motor rotational
speed results in higher machine
performance without an increase
in weight. In so far as possible,
135 V current should be selected
for 200 Hz and 200 V for 300 Hz,
regardless of country.
The secondary power output of
the frequency converter or its size
is calculated as follows: The high-
frequency electric tools to be used
are grouped according to motor
size and number so that their
rated current consumption can
be added together. Multiplying
the sum of the rated current
values by the operating voltage
and the factor ö3 results in a
calculation for the entire apparent
power consumption for the tools.
The formula is:
S =
ö
3 · U · I = 1.73 · U · I
Once the apparent power value
has been calculated in this way,
it must still be multiplied by the
simultaneity factor G in order to
obtain the secondary power out-
put of the converter. The simulta-
neity factor G takes into account
the degree of use of all of the
tools– since the tools are general-
ly not all used at the same time.
ELECTRICAL OPERATING VALUES.
For the simultaneity factor G, we
have the following experiential
values:
automobile body
manufacture 0.45
motor manufacture 0.30
appliance manufacture 0.40
tool and form manufacture 0.25
steel manufacture 0.50
foundry work 0.60
In planning for a high-frequency
electric tool installation, you must
always take into account the need
for a certain amount of reserve
power in the frequency converter.
Particularly for small installations,
you must bear in mind that the
power output must be at least
twice the rated power consump-
tion of the most powerful high-
frequency electric tool to be
connected. This ensures that the
tools will start without trouble.
In the event of short-term over-
load, the voltage drop at the
frequency converter will not be
too large.
A magnetic field forms in a three-
phase current motor, which circu-
lates through the motor. This is
called a rotary field and is depen-
dent on the number of pole pairs
and frequency. When the smallest
possible number of pole pairs is
used, at a frequency of 50 Hz, for
example, a rotary field or rotor
speed of 3000 rpm results; at a fre-
quency of 200 Hz: 12000 rpm and
at 300 Hz: 18000 rpm.
Due to the short distance between
bearings and the stationary stator
coil, the motor is both mechani-
cally and electrically very reliable.
It is distinguished by steady, low-
vibration operation. Speed drop
is only approx. 5% at rated load,
and peak performance is around
21/2 times the rated performance.
Short-term overloads are possible
as long as they do not result in the
admissible coil temperature being
exceeded. Since the objective in
hand tools is to make them as
light as possible with the highest
possible performance, Bosch has
decided in favour of “dust protec-
tion with direct cooling" for its
high-frequency motors (Fig. 2).
This combines the advantages of
both encapsulated and open con-
struction. The flow of cooling air
ensures good heat dissipation; at
the same time, dust and dirt are
prevented from penetrating into
the rotating system.
The design concept underlying
Bosch high-frequency electric
tools offers the user the following
advantages:
Optimum performance in
a light-weight tool
During extended operation, Bosch
high-frequency electric tools
achieve a performance level of
up to 400 watts per kilogram
machine weight. Short-term peak
performance levels reach 2 1/2
times normal operating perfor
mance output. These high reserves
mean a decisive improvement in
work performance.
Constant rotational speed
under load
The speed drop for Bosch high-
frequency electric tools is only
3 – 5% at rated load (Fig. 2).
This ensures that recommended
average speeds can be used to
full advantage during grinding
and drilling. The constant average
speed means that the tools can
be employed more efficiently and
RELIABLE THREE-PHASE CURRENT MOTORS WITH
A LONG SERVICE LIFE.
Fig. 2 Output and rotational speed curve as a function of load moment
Sample calculation for a
high-frequency electric
tool installation
A foundry wishes to introduce
3 high-frequency 0 602 332 034
angle grinders with 230 mm
diameter cutting discs and 3 high-
frequency 0 602 242 134 straight
grinders with 100 mm diameter
grinding discs.
Calculation:
(Refer to pages 24 – 25 and 30 – 31
for current and voltage values)
3 grinders,
motor size 88 3· 10 A = 30.0 A
3 girnders,
motor size 85 3· 6.4 A = 19.2 A
Total: 49.2 A
This yields the apparent power:
S = 1.73 · U · 1
= 1.73 · 200 V · 49.2 A
= approx. 17023 VA
= approx. 17 kVA
This value must still be multiplied
by the simultaneity factor, G = 0.6
for foundries:
Converter apparent power =
S · G = 17 kVA · 0.60 = 10.2 kVA
In this case, a converter with 11 kVA
secondary power is selected so that
there are additional power reserves
of approx. 10 %.
Network groups
Operating frequencies and
operating voltages
Number of
work groups 200 Hz 300 Hz
1 265 V –
2 135 V 200 V
3 72 V (110 V)
4–72 V
7 – 42 V
10 42 V –
Ideal network group is highlighted
Output performance
Peak performance
Rated performance
Speed
Power consumption [W]
Output
perfor-
mance
[W]
Speed
[min
–1
]
achieve a longer service life.
Minimal maintenance cost
combined with high load
capacity
Bosch high-frequency electric
tools offer an easy-to-service
construction design and a motor
without wear parts. Even when
subject to extreme stress con-
ditions (e.g. in foundries), they
live up to their reputation for
long service life at low main-
tenance cost.
Highly effective
Due to their high efficiency levels,
Bosch high-frequency electric
tools offer economical, environ-
mentally compatible operation
under extended operation condi-
tions.