Bosch Power Tools 1375A Sample calculation for a, High-frequency electric, Tool installation

RELIABLE THREE-PHASE CURRENT MOTORS WITH A LONG SERVICE LIFE.

ELECTRICAL OPERATING VALUES.

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.

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.

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

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,

For the simultaneity factor G, we		Sample calculation for a
have the following experiential		high-frequency electric
values:		tool installation
automobile body
manufacture	0.45	A foundry wishes to introduce
motor manufacture	0.30	3 high-frequency 0 602 332 034
appliance manufacture	0.40	angle grinders with 230 mm
tool and form manufacture	0.25	diameter cutting discs and 3 high-
steel manufacture	0.50	frequency 0 602 242 134 straight
foundry work	0.60	grinders with 100 mm diameter
		grinding discs.

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

2 1/2 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

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

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.

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

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-

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:

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

Output	Speed
perfor-	[min–1]
mance	Peak performance
[W]
	Output performance

and the factor ö3 results in a calculation for the entire apparent power consumption for the tools. The formula is:

S = ö3 · U · I = 1.73 · U · I

load, the voltage drop at the frequency converter will not be too large.

S = 1.73 · U · 1

=1.73 · 200 V · 49.2 A

=approx. 17023 VA

=approx. 17 kVA

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:

Speed

Rated performance

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.

Network groups

Operating frequencies and operating voltages

Number of	200	Hz	300 Hz
work groups
1	265	V	–
2	135	V	200	V
3	72 V		(110	V)
4	–		72 V
7	–		42	V
10	42	V	–

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 %.

Power consumption [W]

Fig. 2 Output and rotational speed curve as a function of load moment

Ideal network group is highlighted

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