4

Note the problem specifies the load is "delta connected". There is no neutral connection to measure phase voltage ($V_{LN}$) against. Also note the supply frequency is 60 Hz. 208 V is a common line voltage ($V_{LL}$) in the US (which uses a 60 Hz supply), with corresponding phase voltage of 120 V. You are using a US text (Sarma et al, from another ...


2

The reason is simple - the timing in the evaluation of technology. The required technology to make touchtone signal possible, Dual-tone multi-frequency signaling (DTMF), wasn't developed/introduced by Bell System until 1963, while the rotary technology was made available in 1892 by the American inventor Almon Brown Strowger. Even then, the first dial pad ...


2

Optocouplers are made for milliamperes. You expect a switching circuit where a high current transistor or mosfet is controlled through an optocoupler or other isolation providing part. Such circuits are sold as ready to use components. One for your purposes could have name DC solid state relay with low output voltage drop. The unfortunate fact is that your ...


2

drawing by SSR Because $V_{AB} = V_A - V_B$ (Vector Subtraction). Dashed line is $-V_{B} = -(120 \angle -120° V)$ $= 120 \angle 60° V$. Vector addition of $V_{A}$ and $-V_{B}$ gives line voltage $V_{AB} = 208 \angle 30° V$ In a three-phase, wye connected system the line-to-line voltage (line voltage) $V_{LL}$ ($V_{AB}$, $V_{BC}$, $V_{CA}$) is $\sqrt {3}$ ...


2

Do the assigned homework problems. These will be similar to the exam questions. Other than that, memorize the things you have to memorize.


2

Try to find the exam questions for the past few years (At least two). The source where you find them is a good indicator if you can predict the questions. Usually if you find them from other students or online forums curated by students, chances are that you have some prediction. (some lecturers can limited -- for whatever reason-- in their choice of ...


1

Check past questions if they are available. Do NOT try to predict the next ones, but consider the level of questions asked.


1

Rotary phones were controlled by sending pulses down the line. These pulses were the equivalent of hanging up the phone quickly - hence what you see in old movies and TV shows when they quickly tap the hang-up mechanism to get the operator. In the final versions of rotary phones, you could "dial" by quickly pressing down the hang-up button the ...


1

I believe the method mentioned involves rolling said needle on a charged cloth. Even if both the needle and the cloth become charged, the key is to not discharge them. As you roll the needle, the charge flows around it, causing the same effect as flowing electricity through coils around a stationary needle. The key is not in if but in how. Depends is an ...


1

The consensus seems to be that Vms/krpm is just a spelling mistake, and that the unit meant was Vrms/krpm, i.e. V/krpm for the root mean square voltage. And for the sake of honesty, I have to mention that when starting ST's motor profiler one more time, I can now see Vrms/kRPM. It is just a little hard to distinguish because of the font and size they have ...


1

It may help to recall that the rms value of the sinusoidal waveshape produces the equivalent heating in a resistor as does a straight d.c. voltage of the same numerical value.


Only top voted, non community-wiki answers of a minimum length are eligible