Let's 1st understand what these planets represent on their own?

Rahu - It represents Illusion, Foreign Lands, Foreign Things (foreign as in unknown things. So, for someone living in Punjab, culture and rituals of Kerala is also unknown and hence Foreign), Drugs, Medicines, any type of intoxication, Fame, Wealth, Success, Obsession, Past-life incomplete Desires, Movies, Television, Online World, Cheating, Imagined Fears, Unusual Things, Unique Things, Creativity, Rule breaker. Rahu also blows things out of proportions.

Ketu - Just like Rahu, Ketu also represents Illusion as both are ilusionary planets but the difference is that Ketu is also the one who removes the illusion and brings enlightenment. Besides this, Ketu represents Isolation, Separation, Spirituality, Mystical World, Other Dimension means things related to Alien World, also represents Son, Dog, Intuition, Research Ability, Curious Nature, things which we have already achieved in past life and not much concerned to perform in this life. 

Meaning of Rahu-Ketu Conjunction - This conjunction is not seen in any birth chart or lagna chart but this conjunction is most commonly seen in higher divisional charts. So, if you see your divisional charts beyond D-10 (Dashamsha Chart) then you will find this Rahu-Ketu conjunction in many divisional charts like D-16, D-20, D-24, D-30 & D-40 etc. There are couple of ways to understand that how Rahu-Ketu are conjunct in these charts?

Rahu-Ketu - Normally, Rahu-Ketu are 180* away from each other and seen in exactly opposite houses of birth chart. Rahu represents Materialistic Desires whereas Ketu represents Spiritualistic Desires. They say Rahu is malefic because it is our materialistic desires. By that theory, Ketu should be benefic as it is our spiritualistic desires. Then why Ketu is malefic too? It is because they both represent desires and desire on its own is malefic concept. Desire of anything, may it be desire of God too, shows that we think better than Universe and we know what is good for us and hence we have this desire. Desire itself shows complete lack of faith in God and in his ways. That's why desire by nature is malefic as long as it is attached with something or someone. Hence, Rahu-Ketu both are malefic. 

Also, Rahu represents our obsession and Ketu represents isolation. Rahu is what we are dyeing to get and Ketu is what we don't even want to see. 

Higher Divisional Charts - Divisional Charts after D-10 show our higher conscious level. And this we can see from their representation too. D-16 is for Vehicles/Conveniences, D-20 is for Religious Inclination, D-30 is for Misfortunes, D-40 is for Auspicious Results etc.

Now, understand that we are all born with a nature and many a times in our life we say that it is our nature to act like this, what we can do? But we forget that we all take birth to evolve to next level of consciousness and it is our duty to improve upon our nature. Actually, improving one's nature is also an integral part of same nature. 

Now, Rahu-Ketu together in any chart means your obsession and isolation points are same related to things of that house. When obsession/isolation points are same, It means person has reached kind of neutral-ness related with things of that chart. It means that it doesn't matter to him if he gets things related to that chart or not. It is neither obsession nor isolation. It is a state in between where if person gets it then it is fine and if he doesn't get it then it is fine. Those things don't impact the person any more. 

Another way of looking at it is that with matters related to that chart, person has reached a higher conscious level in this life. Like, if it is in D-30, person had seen so many obstacles or misfortunes in life that he is almost used to it and they won't bother him anymore. If it is in D-20, then person may have gone through such events in life which would have made him religious/spiritual inclined and he would have left everything on God. So, Rahu-Ketu conjunction actually helps the person in reaching higher consciousness related with things of the chart in which it is happening and make him neutral in that area of life. He is neither obsessed nor isolated. Somewhere in between, The Buddhafield. This helps us improving our nature through life & life events, reach a higher consciousness to get a better life next time and move an inch closer to source energy.