schematic knowledge

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Tuesday, May 14, 2013

Calculation of Fault Current Using Impedance Diagram

Let us first illustrate the calculation of the fault current using the impedance diagram with the help of the following examples.

Example

Consider the power system of Fig. 6.8 in which a synchronous generator supplies a synchronous motor. The motor is operating at rated voltage and rated MVA while drawing a load current at a power factor of 0.9 (lagging) when a three phase symmetrical short circuit occurs at its terminals. We shall calculate the fault current that flow from both the generator and the motor.

We shall choose a base of 50 MVA, 20 kV in the circuit of the generator. Then the motor synchronous reactance is given by

per unit

Also the base impedance in the circuit of the transmission line is

Fig. 1 generator supplying a motor load though a transmission line.

Therefore the impedance of the transmission line is

per unit

The impedance diagram for the circuit is shown in Fig. 6.9 in which the switch S indicates the fault.

Fig. 2 Impedance diagram of the circuit of Fig. 6.8.

The motor draws a load current at rated voltage and rated MVA with 0.9 lagging power factor. Therefore

per unit

Then the subtransient voltages of the motor and the generator are

per unit

Hence the subtransient fault currents fed by the motor and the generator are

per unit

and the total current flowing to the fault is

per unit

Note that the base current in the circuit of the motor is

Therefore while the load current was 1603.8 A, the fault current is 7124.7 A.

Saturday, April 13, 2013

Battery Discharger Using Discrete Components

The battery discharger revealed on this web site may be greater with the help of including a Schottky diode (D3). This be certains that a NiCd cell is discharged to not 0.6–0.7 V, but to handiest beneath 1 V as really helpful by means of the producers. An additional impact is then that gentle-emitting diode D2 flashes when the battery related to the terminals is ﬂat. The circuit in the diagram is in protecting with an astable multivibrator operating at a frequency of about 25 kHz. When transistor T2 habitss, a present go with the flows by means of inductor L1, whereupon energy is saved in the resulting electromagnetic container. When T2 is cut off, the ﬁeld crumples, whereupon a counter-emf is produced at a level that exceeds the forward voltage (about 1.6 V) of D2.

$\"Battery$

A present then ﬂows throughout the diode in order that this milds. Diode D1 stops the present ﬂowing via R4 and C2. This course of is halted only when the battery voltage not provides a enough base attainable for the transistors. In the original circuit, this came about at about 0.65 V. The addition of the ahead bias of D3 (about 0.3 V), the ﬁnal discharge voltage of the battery is raised to 0.9–1.0 V. Additional resistors R5 and R6 ensure that enough present ﬂows by D3. When the battery is discharged to the recommended degree, it have to be removed from the discharger considering, unlike the original circuit, a small current continues to ﬂow by D3, R2-R3, and R5-R6 until the battery is fullly discharged.

The flashing of D2 when the battery is nearing beneficial discharge is due to the rising interior resistance of the battery decreasing the terminal voltage to beneath the threshold level. If no current ﬂows, the interior resistance is of no final result since the terminal voltage upward pushs to the threshold voltage with the aid of taking some vitality from the battery. When the discharge is complete to the recommended stage, the LED goes out. It will have to subsequently be mentioned that the battery is discharged adequately when the LED commences to ﬂash.

http://www.ecircuitslab.com/

Friday, April 12, 2013

Using LTC3601 3 3V DC Power Converter

This Dc power converter circuit is designed LTC3601 from Linear Technology and is capable to up to 1.5A output current at a 3.3V. The LTC3601 operating supply voltage range is from 4V to 15V making it suitable for a wide range of power supply applications. The operating frequency of the LTC3601 buck regulator is programmable from 800kHz to 4MHz with an external resistor enabling the use of small surface mount inductors.

The LTC3601 buck regulator can operate in two modes: Burst Mode operation and forced continuous mode to allow the user to optimize output voltage ripple, noise, and light load efficiency for a given application.

Friday, April 5, 2013

Liquid Level Sensor using 741 op amp

This circuit liquid level sensor is using a simple and common operational amplifier IC 741 used as a comparator. When the sensor two-fluid levels (you can use two small pieces of PCB or drivers of some of them) are not found in the fluid of the output voltage of operational amplifier 741 is negative and the T1 is blocked as a result 0 volt voltage resistor R5.

If the liquid level sensor is placed in the fluid of the output voltage of operational amplifier 741 is about a few hundred milli-volts and the transistor T1 conducts, which is an output voltage in the resistance around R5 4 volts.

Monday, April 1, 2013

Touch Switch Circuit Using 555 IC

This is a circuit for touch switch circuit. This circuit is almost same with touch door alarm. This circuit uses a 555 timer as the bases of the touch switch circuit. This is the figure of the circuit.

The operation of this circuit is begin, when the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10 M resistor is on pin 2 causes the circuit to be very sensitive to the touch.

Friday, March 29, 2013

Astable Circuit Produce Pulses Using 555 Timer IC

This is circuit that first introduced by Signetics Corporation as the SE555/NE555 about 1971. Pin connections and functions: (See schematic below for basic circuits). Pin 1 (Ground) – The ground (or common) pin is the most-negative supply potential of the device, which is normally connected to circuit common when operated from positive supply voltages. Pin 2 (Trigger) – This pin is the input which causes the output to go high and begin the timing cycle. Triggering occurs when the trigger input moves from a voltage above 2/3 of the supply voltage to a voltage below 1/3 of the supply. This is the figure of the circuit.

For example using a 12 volt supply, the trigger input voltage must start from above 8 volts and move down to a voltage below 4 volts to begin the timing cycle. The action is level sensitive and the trigger voltage may move very slowly. To avoid retriggering, the trigger voltage must return to a voltage above 1/3 of the supply before the end of the timing cycle in the mono stable mode. Trigger input current is about 0.5 micro amps. Pin 3 (Output) – The output pin of the 555 moves to a high level of 1.7 volts less than the supply voltage when the timing cycle begins. The output returns to a low level near 0 at the end of the cycle. Maximum current from the output at either low or high levels is approximately 200 mA. Pin 4 (Reset): – A low logic level on this pin resets the timer and returns the output to a low state. It is normally connected to the + supply line if not used.

Pin 5 (Control) – This pin allows changing the triggering and threshold voltages by applying an external voltage. When the timer is operating in the astable or oscillating mode, this input could be used to alter or frequency modulate the output. If not in use, it is recommended installing a small capacitor from pin 5 to ground to avoid possible false or erratic triggering from noise effects. Pin 6 (Threshold) – Pin 6 is used to reset the latch and cause the output to go low. Reset occurs when the voltage on this pin moves from a voltage below 1/3 of the supply to a voltage above 2/3 of the supply. The action is level sensitive and can move slowly similar to the trigger voltage. Pin 7 (Discharge) – This pin is an open collector output which is in phase with the main output on pin 3 and has similar current sinking capability. Pin 8 (V +) – This is the positive supply voltage terminal of the 555 timer IC. Supply-voltage operating range is +4.5 volts (minimum) to +16 volts (maximum).

Thursday, March 28, 2013

Phase Shift Oscillator Circuit Using LM386

This is a design circuit of a simple inexpensive amplitude stabilized phase shift sine wave oscillator which requires one IC package, three transistors and runs off a single supply. This circuit is combination with the RC network comprises a phase shift configuration and oscillates at about 12 kHz. The remaining circuitry provides amplitude stability. Here’s the schematic figure of the circuit.

The high impedance output at Q2s collector is fed to the input of the LM386 via the 10 μF-1M series network. This circuit is using op amp LM386 causes it has fixed gain of 20. The 1M resistor in combination with the internal 50 kΩ unit in the LM386 divides Q2s output by 20. The positive peaks at the amplifier output are rectified and stored in the 5 μF capacitor. This potential is fed to the base of Q3. Q3s collector current will vary with the difference between its base and emitter voltages. Since the emitter voltage is fixed by the LM313 1.2V reference, Q3 performs a comparison function and its collector current modulates Q1s base voltage. Q1, an emitter follower, provides servo controlled drive to the Q2 oscillator.